elektor labs

Transcription

elektor labs

magazine
74874
www.elektor.com/magazine
December 2012 | £ 4.90
FPGA
taming the beast
1970’s NAGRA IV Tape Recorder
Arduino AC Grid Analyzer l Electronics 4 Starters
Hyperactive LED Xmas Tree l DIY FPGA Dev system
Internet of Things
Ground Plane
l Missing
Elektor World
What’s cooking @ E-Labs
l PWM to Phase Shifter
AUS$ 14.90 - NZ$ 17.90 - SAR 105.95 - NOK 102
Personal Download for I © Elektor
74874
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countries. All other trademarks mentioned herein are the property of their respective companies. © 2012, Microchip Technology Incorporated. All Rights Reserved. DS31039A. ME1049Eng09.12
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Magazine
Contents
Labs
Community
8
Elektor World
•Elektor Improved Radiation Meter on
ConSat-1… soon
•Elektor Improved Radiation Meter @
Oxford University… soon 2
•Elektor Monster Formant hits YouTube
•Lost in the Electronic Maze
•Circuit Cellar 25th (19hex) Anniversary
Party
•RF Poetry
12 Elektor hot Labs
Clemens Valens on what’s brewing, smelling and burning at Elektor Labs, including
their new website.
14 MIC502 & MAX6643
Raymond’s pick of the month in terms of
components.
16 Tiny but not insignificant
The story of stray capacitance in a FET
preventing a microprocessor from being
programmed.
17 Missing ground plane!? Check
your board with PCB Visualizer
Through a slip-up in one of our circuit
board designs we learned about this
great PCB preproduction checking tool.
18 What’s Cooking?
Not Elektor’s new SMPSU we hope! A look
at an early prototype.
4 | December 2012 | www.elektor.com/magazine
Projects
20 Taming the Beast
An upbeat introduction to FPGAs, followed
by a description of Elektor’s DIY FPGA
Development System.
28 Arduino AC Grid Analyser
This circuit performs a rigorous quality
check on the AC line voltage from the wall
outlet. It’s got FFT and a mini spectrum
analyser, courtesy of an Arduino board.
36 Hyperactive LED Xmas Tree
There’s no end of lively visual patterns
generated by this PIC controlled gizmo,
especially if you build two.
40 Embedded Linux Made Easy (6)
This month the Elektor Linux board gets
connected to a typical home network using
a server application we write ourselves.
46 Arduino on Course (3b)
Can your Android smartphone read sensors directly? Probably not, and that’s
where an Arduino Mega comes in handy.
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Volume 38
–
No. 432
Industry
52 Electronics for Starters (10)
In this tenth and concluding part we
look at basic circuits operating at radio
frequency (RF).
58 Transconductance Amplifier
The principle of converting a differential
voltage into a proportional current allows
a versatile instrumentation amplifier to
be designed and built.
Magazine
66 Creating
a Low-Leakage Rectifier
74 Retronics:
The Nagra IV Tape Recorder
Using a Self-powered Op Amp (Touchstone Semiconductor)
Once the most celebrated portable tape
recorder in the world the Nagra was a
professional device, developed for professional transportable applications; for
broadcast use or picture-synchronized
audio recording; for movies and TV.
Series Editor: Jan Buiting
67 News & New Products
A monthly roundup of all the latest electronics products and components.
78 Hexadoku
64 PWM to Phase Shifter (Design Tip)
Elektor’s monthly puzzle with an electronics touch.
Sure, the function can be carried out by a
few flip flops and gates.
64 Improving the Pick-Up Angle
of an Infrared Satellite Receiver Remote (Design Tip)
Just add a second infrared detector, they
said, but how?
65 Audio Amplifier in Dinner Format (Design Tip)
The TDA7050 has great potential for
making a very compact audio amp.
December 2012
80 Next Month in Elektor
A sneak preview of articles on the Elektor
publication schedule.
Tech the Future
70 The Internet of Things (IoT)
Three experts in electronics industry and
research discuss the origins of IoT and its
impact on today’s electronics.
Series Editor: Tessel Renzenbrink.
www.elektor.com/magazine | December 2012 | 5
74874
Community
Volume 38, Number 432, December 2012
ISSN 1757-0875
All change —
watch the colored dots
Publishers:
Elektor International Media,
78 York Street, London W1H 1DP,
United Kingdom.
Tel. +44 (0)20 7692 8344
www.elektor.com
This edition of Elektor UK .Magazine
(dot magazine) marks the start of
a freshly structured publication.
The changes are not just cosmetic
as is obvious from the categories
called .Community, .Projects,
.Labs, .Industry, and .Magazine you
will have noticed on the restyled
contents pages, but actually
support our vision that the way
electronics is experienced on and
from paper does have a future, and
is online’s best friend in many ways.
Our new membership models introduced last month and progressively
implemented in the course of next year enable you to enjoy these, our
printed pages as much as your PC screen showing the boiler room called
elektor-labs.com. The publication model is simple, too: on the website, feel
free to interact with your fellow readers on all design aspects of projects.
Next, if the Elektor editors and lab workers think it’s really good, the project
and its OP are up for elektorizing, which equates to casting into a prestigious
article printed on paper.
In good e-engineering tradition the machine does not stop there as the
published project hopefully gets directed back to the .labs website, resulting
in feedback, adaptations, discussions, improvements, threats & threads,
FAQs, compile errors, tweaks, and unheard of applications devised by
members from any of the 50 countries and 6 language areas served by
Elektor. That’s the way I’d like to see it work and happen, mainly because I
am into electronic engineering deep enough to say that the stuff that really
matters comes from engineers like you.
The magazine is available from newsagents,
bookshops and electronics retail outlets, or on
subscription.
Elektor is published 10 times a year with a double issue
for January & February and July & August.
Subscriptions:
Elektor International Media,
78 York Street, London W1H 1DP,
United Kingdom.
Tel. +44 (0)20 7692 8344 ,
Internet: www.elektor.com/subs
Email: [email protected]
Head Office:
Elektor International Media b.v.
P.O. Box 11 NL-6114-ZG Susteren
The Netherlands.
Telephone: +31 (0)46 4389444,
Fax: (+31) 46 4370161
Distribution:
Seymour, 2 East Poultry Street,
London EC1A, England.
Telephone:+44 (0)20 7429 4073
UK Advertising:
Elektor International Media b.v.
P.O. Box 11 NL-6114-ZG Susteren
The Netherlands.
Telephone: +31 (0)46 43 89 444,
Fax: +31 (0)46 43 70 161
Internet: www.elektor.com
Advertising rates and terms available on
request.
Copyright Notice
The circuits described in this magazine are for domestic
use only. All drawings, photographs, printed circuit board
layouts, programmed integrated circuits, disks, CD-ROMs,
software carriers and article texts published in our books
and magazines (other than third-party advertisements)
are copyright Elektor International Media b.v. and may
not be reproduced or transmitted in any form or by any
means, including photocopying, scanning and recording,
in whole or in part without prior written permission
from the Publisher. Such written permission must also
be obtained before any part of this publication is stored
in a retrieval system of any nature. Patent protection
may exist in respect of circuits, devices, components etc.
described in this magazine. The Publisher does not accept
responsibility for failing to identify such patent(s) or other
protection. The submission of designs or articles implies
permission to the Publisher to alter the text and design,
and to use the contents in other Elektor International
Media publications and activities. The Publishers cannot
guarantee to return any material submitted to them.
Disclaimer
Prices and descriptions of publication-related items
subject to change. Errors and omissions excluded.
© Elektor International Media b.v. 2012
Printed in the Netherlands
Jan Buiting, Managing Editor
The Team
Managing Editor:
Jan Buiting ([email protected])
International Editorial Staff:
Harry Baggen, Thijs Beckers, Eduardo Corral, Wisse
Hettinga, Denis Meyer, Jens Nickel, Clemens Valens
Design staff:
Thijs Beckers, Ton Giesberts, Luc Lemmens,
Raymond Vermeulen, Jan Visser
Membership Manager:
Raoul Morreau
Graphic Design & Prepress:
Giel Dols, Mart Schroijen
Online Manager:
Daniëlle Mertens
Managing Director:
Don Akkermans
6 | december 2012 | www.elektor.com/magazine
74874
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74874
Community
Elektor World
By Jan Buiting, Managing Editor
Elektor Improved Radiation Meter
on ConSat-1… soon
Hello. I am Michelle Boyce, affiliated with
SpaceConcordia.Ca. We have recently constructed
a Cube Satellite (ConSat-1) for the Canadian
Satellite Design Challenge.
Onboard, one of the payloads is a Solid State
Radiation Detector based on articles from your
magazine:
• Measure Gamma Rays with a Photodiode
Radiation Detector using a BPW34, by Burkhard Kainka, June 2011.
• Improved Radiation Meter Counter for Alpha,
Beta and Gamma Radiation, by Burkhard
Kainka, November 2011.
The project was part of an Educational Outreach
Program with Space Concordia.
Kind regards, Michelle Boyce (Canada)
Our Radiation Meter project was a triumph from
day #1. On reading this message from Canada,
Elektor PR staffers performed a global search
for the wording ‘global coverage” in all corporate documents and replaced it by “global coverage and beyond”. Meanwhile Michelle has been
requested to write an article for Elektor.
row to test or could we
send the one I have
built back (it’s in a
metal box)?
Jeff Lidgard
(UK)
What,
YOU and ‘not
working’? A working prototype is on its
way to you Jeff.
Elektor Monster Formant
hits YouTube
Siegfried Brückner is likely to have the world’s
largest constellation of Elektor Formant modules
on the planet and in space. We estimate the
instrument is about 10 feet wide and 4 feet tall.
It is linked to a sequencer, a bass pedal and a
keyboard. A total of about 110 Formant modules,
500 controls, and dozens red patch cords produce
that inimitable Formant synthesizer sound [1].
Elektor Improved Radiation Meter
@ Oxford University… soon 2
Hello Thijs, I work at the University of Oxford
Physics department. We have been building a circuit similar to yours to go into a
helium balloon to measure cosmic rays.
We bought the radiation detector circuit (we
have tried a few different kits) with hopes to
test it in our lab. We have access to many different sources but have not got your kit working.
I think I have built and shielded it correctly, but
can’t work out what’s wrong with it. It currently
triggers with the comparator set to L68 (above
doesn’t trigger). The signal on K4 looks to be
about 500 mVPP on a scope.
We are quite short of time now but I would still
personally like to see this kit working. If you
would like us to test this circuit with our sources it
possible you have a working circuit we could bor-
Siegfried wrote to us: “Phase #3 of the project
comprises over 160 modules from Elektor’s Formant books 1 & 2, as well as specials and discrete circuits. Everything is connected through a
module wall. An 8-way MIDI interface was incorporated, making the Formant controllable over
MIDI and CV/Gate.
The new Formant keyboard now has a 4th and
5th octave keyboard and additionally a 13-key
pedal. Each keyboard / pedal has a C/V interface.
74874
Elektor World
Rommedal and puzzle creator Sadettin Commert.
Hi friends at Elektor,
I am not sad or mad about not winning, but totally
lost about the answer given as
Input 2. It is
possible,
but with my
l it t l e b r a in
knowledge I
find that Input 1
also is a possible
solution?
This part is taken
from Wikipedia, and I
hope we can agree on
the fact that a Zener is a
normal diode in the arrows
direction :-) ?
The picture shows a hand
drawing of my Input 1 solution.
Would it be possible for you to fast
draw like mine the Input 2 solution
and verify that I’m right or not, and if
not, please show me where is “sleep”.
To be able to
process other sounds
on the Formant, there additional MIDI interfaces were built in.
These allow the keyboards to be played mono
as well as polyphone fashion (expander). Also,
the expander sounds can be modified as required.
In April 2012 I was able for the first time to demonstrate my Monster Formant to fellow specialists
at the Happy Knobbing event in Rheinland Pfalz,
Germany, the theme of the year being: sound
generation using a modular system [2]. The sound
recording unfortunately is below standard. My next
performance is in Munich on November 17.”
Elektor’s own Formant was rescued from a dumpster and gets played occasionally in Elektor Cellar
[3]. Headphones on!
Sincerely, Klavs Rommedahl (Denmark)
(translated from the French)
Dear Jan and Klavs
As it turned out the printed version of the
maze was an early one which contains an error, see
the attached pdf showing the correct version. One
resistor should have been a capacitor! The erroneous drawing thus allows two possible solutions.
KR, Sadettin Commert (France)
[1] http://youtu.be/_5cRr7og4Vc
[2] http://youtu.be/ynQyGT6t9tU
[3] http://youtu.be/JOhxLE3-ecI
Lost in the Electronic Maze
To create a puzzle that has a single solution is
as hard as solving it. See page 78 in the July
& August 2012 edition. Over to reader Klavs
74874
Community
Circuit Cellar 25th (19hex)
Anniversary Party
ner, speeches and chats not just with current and
former CC staffers, but also with many of their
renowned columnists and project editors including
Ken Davidson, Dave Tweed, Robert Lacoste, Ed
Nisley, and Jeff Bachiochi. With CEOs, SFOs etc.
well out of hearing range the conversations soon
turned electronic & embedded. Sincere thanks
go out to party hosts Steve Ciarcia
and Hugo Van haecke.
RF Poetry
September 28 and 29 2012
marked the twenty-fifth anniversary of Elektor’s truly awesome sister
magazine Circuit Cellar. Your editor was fortunate
to be invited over to New Castle NH, USA for dinAdvertisement
My thanks go out to the crew at the Robert Frost
Farm, Derry, NH, for awarding me a pencil for
no more than citing one line of RF poetry: “One
could do worse than being a swinger of birches”.
Back at my desk at Elektor HQ I am using the
pencil to scribble edits as well as draw the odd
circuit diagram when our main servers are down.
74874
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labs
By Clemens Valens
(Elektor .Labs)
Don’t miss the hype
When I was a student the teachers often said that it was hard to keep up with advancing technology. I thought
“well, is it?” as I did not find it difficult at all to consume all the information I could find. But now that I am
about to lose the last hair on my head and my muscles are getting weak, I must admit that it is not an easy task
to constantly know what is going on in every corner of techno land. Luckily I am not alone and some people are
even worse off than I.
The other day I shared a ride with an even older colleague. Since he was driving I was watching the road signs
and when we got close to our destination I pulled out my phone to have a look at Google Maps. The phone was
sleeping so I had to activate it first and for this I have to slide my finger over the display in a special pattern, like
a signature. This is called a pattern lock. My colleague saw me do this and was so amazed that he almost crashed
into another car. Back on the road again he asked me if what I just did was the latest in cool gadgets. I said that
it wasn’t and that I had seen people using it for several years now. Actually, I said, we have a project on the .LABS
website that shows you how to build your own pattern lock. My driver was deeply impressed.
Funny though, just three days later I received a message from the guy that was doing this project on .LABS,
announcing that it was ready. He had even posted a promotional video, did I get a chance to see it? I hadn’t been
to his project page in a while, so I looked it up again and now it was time for me to be deeply impressed. Nice clean
write-up, high-quality photographs, excellent video, exactly as we like it. His presentation immediately made me
want to build one myself. You will not be surprised to read more about this project soon in the printed magazine.
Of course it would be great if all the projects on .LABS were so well presented, but it is not at all mandatory. If
you don’t have the equipment to take studio-quality photos, then use your phone. If you don’t have the time to
draw a circuit diagram in a professional CAD package, simply sketch it on a piece of paper and upload a scan.
The only thing we care about is that you take the time to come up with neat projects and great ideas. Blow us
over and we will reward you.
Have a look at the pattern lock project and build your own:
www.elektor-labs.com/project/android-style-capacitive-sensing-pattern-lock.12407.html
The origin of a species
I just love Wikipedia, don’t you? Look what I discovered some time ago:
“Psocoptera are an order of insects that are commonly known as
booklice, barklice or barkflies. They first appeared in the Permian
period, 295–248 million years ago. They are often regarded as the
most primitive of the hemipteroids. Many of these species have only
been described in recent years.
The largest suborder are the Psocomorpha, with about 3,600 species
in 24 families, ranging from the species-poor Bryopsocidae (2 species) to the speciose Psocidae (about 900 species). Psocomorpha are
notable for having antennae with 13 segments. They have two- or
three-segmented tarsi, this condition being constant (e.g. Psocidae)
or variable (e.g. Pseudocaeciliidae) within families.”
If, like me, you didn’t understand most of that, rest
assured that it’s about bugs.
So why mention them here?
Because recently the suborder of Psocomorpha has been
extended with a new species,
the noisiest of all, the PSoCaMorph music synthesizer.
It was first discovered
on .LABS, and I think
that this is very cool.
The goal of the project is to design an oldfashioned analog music
synthesizer using modern Programmable System-on-Chip (PSoC) technology. As you have surely understood from the first bit of this article,
bug families are highly modular; the species are constructed from
wings, leg and antenna segments and other body parts. Analog music
synthesizers are also modular; they consist of one or more VCO, VCF
and VCA modules and some other parts. Insects can be collected and
stored in special envelopes; analog synthesizers have envelope generators. Chips, like bugs, are small and annoying but they have more legs.
Psocoptera appeared some 250 million years ago, analog synths are
vintage too. So a modular synthesizer in a chip is almost a bug, right?
Anyway, what I wanted to tell you is that U2 can now get into insectology by joining the PSoCaMorph project on .LABS. If you do so, you may
even win a PSoC 5 Development Kit, all you have to do is contribute.
The PSoCaMorph lives here:
www.elektor-projects.com/project/the-psocamorph.12269.html
74874
elektor H T labs
EDITOR’S
CHOICE
Editor’s Choice
A number of .LABS projects have been selected by our editors and should be up for
publishing in the near future. For some of these projects, sadly we found that the
original poster (OP) does not reply to our messages. Therefore, if you posted a project,
please check on a regular basis the email account you used to access .LABS. We will not
get you in publication if we cannot get in contact with you. Here is a selection of projects
that we think are interesting and that we would like to publish in the printed magazine:
Geiger Counter Data Logger with WLAN Interface
OP Marcus Vohburger is working on a complete system for measuring and monitoring radioactivity.
According to him, building a Geiger counter is actually pretty simple. Because it is so simple he added
some extra stuff.
www.elektor-projects.com/project/geiger-counter-data-logger-with-wlan-interface.12264.html
elektor
labs
Mains Gate:
Programmable Relay & Energy Monitor
The OP John Hind writes about this project: rather than some US political scandal, this is an idea
for “mashing up” five of the circuits from the July & August 2012 double issue to produce a really
flexible “mains gatekeeper” circuit combining a multitude of control, measurement, protection
and logging functions at minimal cost.
www.elektor-projects.com/project/mains-gate-programmable-relay-energy-monitor.12461.html
Simple MIDI Wind Instrument
This is based on early experiments done by the OP that ended in an overly complex system. If we publish this project it
would be a modernized and simplified version. We could do with a bit of help from you to come up with a usable wind
instrument slash air pressure sensor.
www.elektor-projects.com/project/simple-midi-wind-instrument.12277.html
Wind Direction and Speed Instrument
Sandwiched between two spray-can caps sits a little PCB with only four parts: a purposely
overheating transistor and three NTC resistors. Wind will blow the column of hot air produced by the transistor out of the centre; this change of position is picked up by the NTC
resistors. Neat, don’t you think?
www.elektor-projects.com/project/wind-direction-and-speed-instrument.12480.html
74874
Labs
Component Tips
By Raymond Vermeulen (Elektor Labs)
MIC502 and MAX6643 Fan-Speed Controllers
For this month’s instalment I researched two ICs that provide stand-alone functionality as fan-speed controllers. This can be very handy when you
have a system which is dissipating a lot of power, but is also built into some kind of enclosure. This makes forced-cooling with a fan a necessity. If
you would like to make the control of this fan dependent on the temperature, but don’t want to delegate this task to the existing microcontroller,
then a separate control IC will be very useful. You only need to connect a sensor and a fan. One striking detail is that the ICs presented here do
not follow the standard 4-pin, 25 kHz PWM fan speed control, but switch the power supply voltage directly at much lower frequencies.
(120569)
MIC502
MAX6643
The MIC502 made by Micrel uses an NTC or PTC as the temperature sensor, with the option of having a second sensor. The sensors are connected to inputs VT1 and VT2. A voltage from about
30% to 70% of Vdd produces a duty cycle of 0% to 100%. The
highest of the two inputs takes precedence, which is a very nice
feature if you use one sensor to measure the ambient temperature and use another to monitor the temperature of a component that is likely to get hot. A voltage can be applied to the Vslp
pin, which causes the chip to go into a sleep state when both
inputs VT1 and VT2 drop below this value. When either VT1 or
VT2 go above this value then the IC will be reactivated. This is
mainly to avoid the fan stalling at a duty cycle that is too low for
it to operate properly. A timing capacitor is connected to pin CF,
a value of 100 nF is recommended for a frequency of 30 Hz. You
can, however, also set a higher frequency. According to the data
sheet the range is from 15 to 90 Hz.
The MAX6643 uses a diode-connected transistor to do the temperature measurement. This IC has three different temperature
control settings. The temperature is set (between 60 and 100 °C)
with the ‘Overtemperature Threshold’ inputs (pins OT1 and OT2)
and the OT-output will be activated when this temperature is
exceeded. The ‘High temperature Threshold’ inputs (pins TH1
and TH2) determine at which temperature the duty-cycle of
the PWM-signal increments by one step. The ‘Low temperature
Threshold’ inputs (pins TL1 and TL2) determine the temperature
at which the duty cycle of the PWM signal goes down by one
step. For each of these temperature-thresholds a number of different values can be set by connecting the corresponding pins to
Vdd or GND or leave open (refer datasheet).
Figure 1. Block diagram of the MIC502.
Figure 3. Block diagram of the MAX6643.
Figure 2. Application example using the MIC502.
Figure 4. Application example using the MAX6643.
MIC502 datasheet: www.micrel.com/_PDF/mic502.pdf
There is also a ‘FULLSPD’ pin, to force a duty cycle of 100%. This
can be useful when an excessive temperature has been detected.
In addition there is an input for the tacho signal from the fan,
which allows the ‘FANFAIL’ pin to indicate when there is a problem with the fan.
MAX6643 datasheet: http://datasheets.maximintegrated.com/en/
ds/MAX6643-MAX6645.pdf
74874
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74874
Labs
Tiny but not insignificant!
by Dr. Thomas Scherer (Germany)
This circuit refuses to be programmed by an
AVRISP MKII programmer; can anyone see why?
I must admit to spending too many hours recently
trying to answer that simple question. First some
background: My plan was to make a simple, flexible but precision balancing circuit for my newly
acquired LiFePo battery pack. Off-the-shelf solutions using expensive specialist ICs would do the
job but I like to take a more practical approach.
This seems like an ideal application for a tiny
low-cost AVR microcontroller. I am already familiar with the ATtiny25 (see [1] and [2]) so I was
feeling quite confident as the design took shape.
Little did I suspect that I would fall at the first
hurdle when I tried to flash the firmware to the
controller.
My first thoughts turned to the layout but after
checking and double-checking the PCB tracks
+VB
K1
D1
8
VCC
C1
1u
PB0(MOSI)
PB1(MISO)
PB2(SCK)
PB3(ADC3)
4
GND
PB4(ADC2)
PB5(RESET)
10k
5
MOSI
6
MISO
7
SCK
2
C2
2
3
4
5
6
100n
To reduce its influence, resistor value (R6) was
increased to 10 kΩ. Now when I plugged the
AVRISP cable into K3 and clicked on ‘Program’
in AVR studio everything ran as it should and the
flash was successful. I am really quite happy to
admit to my errors; after all as someone once
said, experience is just the name we give to our
mistakes.
[1] www.elektor.com/magazines/2011/january/
all-soft-555.1642210.lynkx
R2
ISP
–VB
Perhaps the loading of the 1 kΩ resistor R4 in
series with LED D1 was affecting a programming
signal? But no, that was also a red herring; pin 2
(PortB.3) doesn’t even have a connection with
K3. Now my attention focused on the switching
MOSFET T1, although small in stature, this could
in fact have a significant amount of capacitance
associated with its input; maybe even enough
to load the digital programming signal? A quick
look at the data sheet confirmed my suspicions:
Ciss = 900 pF… bingo!
(120429)
K3
1
1M
330k
K2
R3
TSM2312
J1
RESET
1
2W
R6
1k
2
3
2W
T1
1
ATTINY25
2W
R10
10R
R7
R9
10R
R5
10k
R4
1k
1M
R1
IC1
10R
R8
and component placement the finger of suspicion
began to point to the microcontroller. Maybe the
manufacturer had sent out a batch with the SPIEN
fuse bit disabled? That would of course prevent
any attempt to flash using the ISP/SPI route. My
use of an SMD outline microcontroller made it
difficult to directly connect to a STK500 programming board to work round the serial interface
and try ‘high voltage’ programming. Once again,
with leads directly soldered from the HV pins on
the STK500 to the PCB programming failed even
though HV programming should always be possible. The plot was definitely starting to thicken;
to simplify things even more I soldered flying
leads onto the SMD ATtiny25 package to directly
connect it to a DIL socket on the STK500. This
time programming was successful and the SPIEN
fuse on the chip was found to be correctly set all
along. There must indeed be something wrong
with the circuit, but what?
120429 - 11
[2] www.elektor.com/magazines/2008/january/
anti-standby-switch.321677.lynkx
74874
E-labs Inside
Missing ground plane!?
By Thijs Beckers (Elektor Editorial & Labs)
Not everything went smoothly as lab worker Luc
was working on an aviation radio scanner project. Several components used by the author
were no longer in production, albeit they would
probably still be available from selected retailers
and old stock vendors. So to ensure the project
can be replicated by readers for some time in
the future, a number of components had to be
replaced with modern ones. Laying out the PCB
(with the new components) and ordering all the
components needed for the prototype build-up,
however, went without a hitch. Until the proto
PCB arrived in the post.
Check your board with
PCB Visualizer!
Somewhere during the design process using our
CAD software suite Altium Designer, Luc ‘shelved’
(hid) the top and bottom ground planes in order
to have a better overview on the routed signals.
When finished, he generated the Gerber files for
the proto PCB production using our standard .outjob file and sent them off to our long term proto
supplier Eurocircuits [1]. No errors were flagged
during the process and it wasn’t until Luc received
the PCBs in the mail that he saw the shelved
ground planes were missing on the physical board
(see the pictures). This rendered the PCB useless,
since a lot if not all of the ground connections were
laid out using the ground planes.
Backtracking his actions, he remembered shelving
those missing planes. As it turned out, everything
that’s shelved gets omitted from the Gerber files.
Of course this could have been prevented by having a look at the files with a Gerber viewer program before they were submitted for production,
but time pressure and distraction by other duties
got into the way of this extra verification step.
Having discovered the error, Eurocircuits’ new service ‘PCB Visualizer’ (see screenshot) was mentioned as a possibly better checking option than
the Gerber viewer software our labs had been
using. This online utility accepts your uploaded
files (Extended Gerber or CadSoft Eagle V6) and
conveniently displays a preview of what the PCB
will look like after production. Any design error
or ordering mistake can be nipped in the bud at
this moment, as an extended overview of parameters is displayed on the left, while the board
can be viewed in detail on the right.
After you confirm that everything is as it is designed
to be, the board can be ordered and the PCB can
be expected to arrive in the mail, manufactured
according to your exact specifications, hopefully without any missing tracks, copper pours or
polygons.
(120568)
Internet Link
[1] www.eurocircuits.com
74874
Labs
What’s cooking?
Not Elektor’s new SMPSU we hope!
s u i ta b le
a n s fo r m e r
tr
n
io
t
la
o
Is
is s e r ie s
2 3 0 VA C ; th
d
n
a
115
r
fo
t fo r
a l fo o tp r in
ic
t
n
e
id
n
a
in g s .
uses
o u tp u t r a t
r
e
w
o
p
t
n
e
d if f e r
n ie n t.
Ve r y c o n v e
h ig h
a r e s p e c ia l
T1 and T2
X P w i th
Ts f r o m N
current FE
).
lo w R D S (o n
e x tr e m e ly
era b a r e ly s o ld
IC 1 a n d IC 3
ge. S t ill m a n a
b le b y h a n d
of
g h th e u s e
a b le , a l th o u
io n
e w o r k s ta t
a h o t a ir r
.A
e
d
c om m e n d
is h ig h ly r e
id e a l
n w o u ld b e
r e f lo w o v e
.
fo r th is jo b
le
is s e le c ta b
Reset mode
h
ic c u p , la tc
w i th J P 2 (h
y -c y c le )
o f f, c y c le -b
0 .0 .1’ o n th e
N o te th e ‘v
b o ard .
Fine tuning of the f eedback
f il ter (C5, C6, R5, R28) is
determined experimentally.
74874
E-labs Inside
A new project is taking shape in our Elektor Labs. In the capable hands of designer Ton Giesberts
a switch-mode power supply (SMPSU) is now being devised and has made it to its early proof of
concept stages. Let’s have a sneak peek…
By Thijs Beckers (Elektor Editorial & Labs)
Deep down
t h e s u p p ly
is a
current mo
de Buck co
n v e r t e r.
D u a l la y e r
P C B.
J P 3 p r o v id
e s th e o p t io
n
to c h o o s e b
e tw e e n h a r
d
wa r e a n d / o
r s o f tw a r e
c u r r e n t lim
i t in g .
In te r fa c e to
m ic r o c o n tr o lle r ; s o f
tw a r e a n d
des ig n to b e
im p le m e n te
d.
IC 3 h a s i ts
N C p in s s h
or t
c ir c u i te d b
y tr a c k s .
To b e in v e s
t ig a te d .
T 6 : s e c t io n
te m p o r a r ily
im p le m e n te
d fo r p u ls e
d
lo a d te s t in
g purposes
C17 has specs by design, which are only met by a special Nichicon cap. Availabili ty?! ESR measurement resul ts
on C17 were unsat isfactory (0.4xx ohms). Measurements conducted ‘the old fashioned way’ were inconclusive at
f irst. It turned out to be a ground loop between the measurement devices messing up the measurements.
74874
Projects
Taming the Beast
A simplified approach
to working with FPGAs
Text:
FPGAs are unquestionably among the most versatile but complex components
(Elektor Labs)
in modern-day electronics. An FPGA contains a maze of gates and other circuit
Design:
elements that can be used to put together your own digital circuit on a chip. In
(Elektor Labs)
this series of articles we use an FPGA development board designed in the Elektor
Clemens Valens
Raymond Vermeulen
Labs to show how easy it is for any electronics enthusiast, whether professional or
amateur, to work with these programmable logic devices. If you’ve been afraid to
tackle FPGAs, you can relax now with the Elektor FPGA board.
The abbreviation ‘FPGA’ stands for ‘field programmable gate array’. FPGA devices might better be
described as user-configurable logic, since that’s
what it comes down to. An FPGA contains a large
number of logic gates, flip-flops and memory elements (as well as quite a few other things) that
can be configured by the user to form a circuit.
The main difference between FPGAs and micro-
74874
Elektor FPGA Dev Board
processors or microcontrollers is that FPGAs do
not execute programs (they are not processors),
but instead should be regarded as circuitry.
Figure 1.
A simple block diagram
representation of a logic cell
in an FPGA.
It all started with a simple array
The first programmable logic devices consisted
of arrays of a few dozen logic gates whose inputs
and outputs could be linked together more or
less as desired. This makes it relatively easy to
implement complex logic functions in a single
IC instead of using a large PCB with lots of individual logic ICs. Another benefit of this approach
is that it allows functions to be modified quickly
by reconfiguring the IC, with no need to cut PCB
tracks and make new physical connections. This
type of programmable logic closely resembles
read-only memory (ROM) or erasable programmable read-only memory (EPROM), which offer
similar capabilities. To take a simple example,
consider an AND gate with two inputs (A and B)
and one output (Q). The truth table of this gate is:
A
B
Q
0
0
0
0
1
0
1
0
0
1
1
1
If you rename the A and B inputs to A1 and A0
and the Q output to D0, you have a data line and
two address lines that can be used to access four
memory locations. If you then store the values
0, 0, 0 and 1 in the memory locations, you have
an AND function in memory. You can also store
different values in the memory, and you can use
a different number of addresses. This is a fairly
simple way to implement a complex logic function.
However, what you can’t do in memory is to
store the result of an operation somewhere else
in memory. Even if the memory has many registers, it cannot access itself. Only the user can
write data to the memory or read data from the
memory.
Consequently, programmable logic was extended
to include registers for storing results, so that
they could be used somewhere else on the chip.
What we mean by ‘registers’ here is ordinary
flip-flops, which are one-bit memory cells. Figure 1 shows a simplified version of the logic cells
used in FPGAs.
You can do quite a bit with flip-flops, especially
if you have a lot of them. For example, you can
build counters and registers, such as 8-bit registers or registers of any desired width. You can
also implement shift registers, which makes it
possible to perform serial to parallel conversions
(and the other way round) or delay digital signals. In short, an array of logic gates is nice,
but it becomes truly attractive when you add
memory elements.
Boosting the complexity
with more options
In the course of time programmable logic became
increasingly complex, as can be seen from the
designation ‘complex programmable logic device’
(CPLD). Technological progress also made it possible — or perhaps better put, necessary — to
design the devices to more closely resemble
random access memory (RAM) than read-only
memory (ROM). RAM cannot retain data without power, and this property is shared by these
programmable logic devices – every time the
power is switched off, the device configuration
is lost. It was therefore necessary to be able to
configure the devices on start-up without using
special programming hardware – ‘in the field’,
as it were. This marked the birth of FPGAs. To
simplify the configuration process, the configuration data is often stored in external nonvolatile
memory and read out by the FPGA during startup. This is highly reminiscent of a microprocessor system, which also reads its software from
external memory. Incidentally, FPGAs that can
retain their configuration are also available now.
Over the years FPGA manufacturers have managed to put an enormous number of gates and
flip-flops on a single chip. This constantly increasing level of integration makes new applications
possible, as well as extremely high data rates,
but it also causes new problems in areas such as
chip layout. The ability to arbitrarily link several
million ports requires a lot of interconnects. Some
of these interconnects can become relatively long,
for example if the output of a gate in the upper
left corner must be connected to an input in the
74874
Projects
Figure 2.
A digital filter consists of a delay line, multipliers and
adders. The synchronizing clock signal is not show
here. The delay line can be built using registers, the
constants are stored in registers, and the multipliers
and adders consist of logic functions and registers.
register
register
C0
C1
register
Cn-1
register
Cn
All of this can easily be implemented in an FPGA,
which is why FPGAs are so suitable for digital signal
processing applications.
bottom right corner. These distances can create
problems at high data rates with correspondingly
short pulse lengths. Propagation delays become
significant, pulse edges are no longer aligned,
and it is increasingly difficult to keep the gates
synchronized with each other.
This has led to an overall FPGA architecture that
is divided into function blocks. The positioning of
the blocks on the chip is carefully chosen to allow
them to be used optimally in most standard applications. Special functions are sometimes available
for special applications, which means that FPGAs
are not all created equal. The blocks present
in every modern (but with various names) are:
Along with these general functional blocks, FPGAs
may also contain processor blocks, flash memory,
and peripheral devices such as Ethernet controllers, memory controllers, ADCs and serial communication controllers for SPI, I²C, etc. With all
these extra functions, FPGAs are heading in the
direction of complete systems, which is sometimes called 'system-on-chip (SoC) with FPGA'.
The blocks can be interconnected using a flexible
system of configurable links.
• Logic blocks
• I/O blocks
• Computation blocks
• Memory blocks
• Clock blocks
Logic blocks
Logic blocks occupy most of the area of the FPGA
and are referred to as the ‘fabric’ of the FPGA.
In a manner of speaking, the applications are
woven on this fabric. The example described at
the start of this article belongs to this block category. A logic block is a configurable arrangement of gates and registers based on a look-up
table (LUT) architecture. The LUTs have the same
operating principle as the previously described
AND gate, but are usually larger and have more
inputs. A LUT can be regarded as an n-bit register
(e.g. 16 bits) that can be used to perform logic
operations. It is also possible to use the LUTs
as shift registers. In addition, the LUTs can be
used as memory, in which case they are called
‘distributed RAM’ to distinguish them from the
memory blocks. With the addition of a few multiplexers and some glue logic, the versatility is
increased and the logic block can also do a bit
of computation.
Table 1. Functional blocks of the Xilinx
Spartan 3E XC3S250E-4VQG100C.
Gates
250,000
Logic blocks
612
I/O blocks
66, of which 7 input-only
Computation blocks
12 multipliers
Memory blocks
12, with a total of 221,184 bits
(216 Kbit)
Distributed memory
39,168 bits (38.25 Kbit)
Clock blocks
4
The number of I/O blocks depends on the device package. We chose the VQ100 option
with 100 pins. A logic block, which Xilinx calls a ‘configurable logic block’ (CLB),
consists of four slices. Each slice contains two 16-bit LUTs, half of which can be used as
distributed RAM. The other half is for logic functions. Each slice also has two flip-flops,
so each CLB has a total of eight flip-flops (see Figure 3).
The blocks
Let’s have a closer look at the previously mentioned functional blocks.
Since the FPGA has so many blocks of this sort,
you can configure several of them in parallel to
form a multiplier or an adder. A digital filter con-
74874
sists of a number of memory elements, a few multipliers and an adder, and digital Fourier transform
logic has the same basic recipe (see Figure 2).
This means that logic blocks contain all the basic
ingredients you need to put together digital filters
or Fourier transform stages. Although this can’t
be done with a single logic block, it is readily
possible with several blocks. This makes FPGAs
especially suitable for digital signal processing.
If you fit an FPGA between an ADC and a DAC,
you can do really nice things with audio, video,
radio or what have you — and with several channels at the same time.
FPGAs with over a million logic blocks are currently available, such as the Xilinx Virtex-7
XC7V2000T with 1.2 million LUTs and 2.4 million flip-flops. This IC contains nearly seven billion transistors. For comparison, Intel’s ten-core
Xeon Westmere-EX processor contains a paltry
2.6 billion transistors.
I/O blocks
The logic blocks on the chip, as well as the other
functional blocks, need to be able to communi-
cate with the outside world via the pins of the IC
(the previously mentioned XC7V2000T has 1200
pins). The communication paths are provided by
the I/O blocks.
An I/O block is more than just a pair of transistors in push-pull configuration. I/O blocks support a variety of communication protocols (DDR,
PCI, LVTTL, LVCMOS, LVDS, etc.) as well as single-ended and differential signals, and they can
achieve extremely high data rates.
For this purpose they are equipped with delay
lines, synchronization flip-flops and parallel/serial
converters (collectively known as SerDes, which
is short for serialiser–deserialiser). Pull-up and
pull-down resistors are also present, and termination resistors are often included.
The I/O blocks are arranged in banks, each of
which has its own supply voltage. This allows different banks to support different communication
protocols, which enhances the versatility of the
FPGA. To reduce current consumption and keep
electromagnetic radiation within reasonable lim-
Figure 3.
Block diagram of part of a
slice. The missing part is the
bottom portion. It is largely
the same as the part inside
the dashed line, which is
called the top portion.
74874
Projects
The circuit
As can be seen from the block diagram in Figure 4, the circuit primarily consists of an ATmega32U4 microcontroller,
a Spartan3e FPGA, a power supply section and a MicroSD
card socket.
The main component is the FPGA (see also the full schematic diagram in Figure 5). We decided to use the Xilinx
XC3S250E-4VQG100C, a member of the Spartan3e family.
It has 250,000 system gates, over 5,500 logic cells and 612
logic units, and the maximum clock frequency is 572 MHz
(see also Table 1). We looked for an FPGA with a small
package in order to keep the board dimensions compact.
The device we selected is housed in an SMD package with
100 contacts, of which 66 are I/O contacts (enough for most
applications). The amount of logic on board is sufficient for
even fairly complex projects.
to +3.3 V by pull-up resistors to prevent the occurrence of
undefined states. There is a card-detect switch that indicates
whether a card is inserted in the socket.
The power supply section is rather elaborate for a circuit of
this size. This is primarily because the FPGA needs three different supply voltages: 3.3 V, 2.5 V and 1.2 V. The MicroSD card
and the microcontroller are also powered from the 3.3 V rail.
Extra capacitors are included to ensure stability and decouple
the different supply voltages.
The board is powered from the USB port if a jumper is fitted
on JP1. This +5 V supply voltage is also available on pin P26
of connector K5 on the card edge for external use. Caution:
The I/O connections on the board cannot withstand +5 V.
The board can also be powered locally if the jumper is not fitted on JP1. In this case an external +5.5 V power supply can
be connected to pin P26 of connector K5, eliminating the need
for a USB connection.
Due to the large number of signal lines and supply planes, it
was necessary to design a four-layer board for this project
(Figure 6). However, this doesn’t create any problems for
users, since a fully assembled board can be ordered from the
Elektor Shop at a very reasonable price.
An unusual configuration method
Figure 4.
Block diagram of the Elektor FPGA development board. The main
components of the circuit are an FPGA, a microcontroller and a
connector for a MicroSD card.
The ATmega32U4 microcontroller handles the control tasks
on the board. It supports communication with a PC via USB,
provides a virtual COM port, and allows the PC to treat the
MicroSD card as a mass storage device. It also reads the data
from the MicroSD card and programs the FPGA. We selected
this microcontroller because it combines familiar ATmega
technology with USB hardware. Although it’s a relatively slow
8-bit device, it’s perfectly adequate for this application. As
usual, the firmware for the microcontroller is available on
the Elektor website [1], and the microcontroller on the fully
assembled board supplied by Elektor is pre-programmed.
The MicroSD card socket was chosen specifically for its small
footprint. It is wired for use in SPI mode, which is supported
by most MicroSD cards. The two unused I/O lines are tied
FPGAs usually do not support nonvolatile programming, so they
must be configured anew each time the circuit is powered up.
With most FPGA development boards this is done with the aid
of a PC and a JTAG programmer, which is also possible here
via connector K3. Operational devices with FPGAs often use
flash memory connected to the SPI bus to hold the configuration data. During the start-up process, the FPGA reads the
configuration data from the flash memory.
Here we take a completely different approach, as illustrated
in Figure 4. We use a microcontroller that utilizes the SPI
protocol to load the configuration data into the FPGA. This is
called Serial Slave mode. This mode is normally used in large
systems with multiple FPGAs, but it can also be used with just
one FPGA.
The microcontroller can communicate with the MicroSD card
over the SPI bus. This card must be formatted in FAT16 or
FAT32 format to allow it to be used with an operating system.
Consequently, the microcontroller must be able to work with
this file system in order to read a file from the MicroSD card.
74874
C16
C25
C26
C27
C28
C18
C33
C17
C32
C35
C20
C34
C19
C29
C30
C31
C13
C14
1u
6V3
1u
6V3
100n
16V
100n
16V
100n
16V
100n
16V
1u
6V3
100n
16V
1u
6V3
100n
16V
100n
16V
1u
6V3
100n
16V
1u
6V3
100n
16V
100n
16V
100n
16V
1u
6V3
1u
6V3
92
78
LED1
K2
SD_SOCKET
79
820R
47k
100n
16V
R11
R12
820R
C24
10u
6V3
47k
C4
R4
LED2
L02P_0
83
L02N_0
84
L03P_0
85
L03N_0
86
88
89
90
NC/DAT2
CS/DAT3
DI/CMD
VDD
SCLK/CLK
VSS
DO/DAT0
94
L06N_0
95
98
P5
SCLK
HSWAP
MISO
PROG-B
P7
DONE
P8
TDO_FPGA 76
TCK_FPGA 77
CARD_DETECT
TDI_FPGA 100
69
P1
P2
MISO
L01P_1
53
L01N_1
54
L02P_1
57
SCLK
L02N_1
58
P4
MOSI
L03P_1
60
P5
RESET
L03N_1
61
L04P_1
62
P3
P6
63
VCCO_2
20
VCCO_3
VCCO_2
VCCO_3
VCCAUX
VCCAUX
31 45 8
VCCAUX
VCCINT
VCCAUX
VCCINT
VCCINT
VCCINT
VCCO_1
21 46 74 96
34
IO/D5
IO/M1
IO_L01N_0
IO_L02P_0/GCLK4
IO_L01P_2/CSO_B
IO_L02N_0/GCLK5
IO_L01N_2/INIT_B
IO_L03P_0/GCLK6
IO_L03N_2/D6/GCLK13
IO_L05P_0/GCLK10
IO_L04P_2/D4/GCLK14
BANK 2
IO_L05N_0/GCLK11
IP_L05N_2/M2/GCLK1
IO_L07P_0
IO_L06P_2/D2/GCLK2
IO_L07N_0/HSWAP
IO_L06N_2/D1/GCLK3
IO_L07N_2/DIN/D0
IO_L08P_2/VS2
TMS
IO_L08N_2/VS1
TDO
IO_L09P_2/VS0
TCK
IO_L09N_2/CCLK
3
CLK_O
C5
35
SCLK
36
MOSI
10u
6V3
1
IN
4
C7
2u2
6V3
M2
40
MISO
IC6
OUT
TLV70225
DBV
3
39
EN
NC
+2V5
5
4
C8
GND
2u2
6V3
2
43
M0/SCL
44
MOSI_1
47
MISO_1
48
L08N_2
49
L09P_2
50
CCLK
C6
10u
6V3
1
IN
IC7
OUT
TLV70233
DBV
3
IP
IO_L01P_1
IO_L01P_3
IO_L01N_1
IO_L01N_3
IO_L02P_1
IO_L02P_3
IO_L02N_1
IO_L02N_3/VREF_3
IO_L03P_1/RHCLK0
IO_L03P_3/LHCLK0
IO_L03N_1/RHCLK1
13
EN
NC
+3V3
5
4
C9
2u2
6V3
IO_L03N_3/LHCLK1
BANK 3 IO_L04P_3/LHCLK2
+3V3
IP
K5
2
L01P_3
3
L01N_3
P50
4
L02P_3
P49
5
L02N_3
TCK_AVR/ADC4
P48
9
L03P_3
TMS_AVR/ADC5
P47
10
L03N_3
TDO_AVR/ADC6
P46
11
L04P_3
TD1_AVR/ADC7
P45
12
L04N_3
L01P_2
P44
15
L05P_3
L07N_3
P43
16
L05N_3
L07P_3
P42
17
L06P_3
L06N_3
P41
18
L06N_3
L06P_3
P40
22
L07P_3
L05N_3
P39
23
L07N_3
L05P_3
P38
IP
P37
L04N_3
P36
L04P_3
P35
P7
L08N_2
P8
L09P_2
L05P_1
65
P9
L01P_1
L05N_1
66
P10
L01N_1
L06P_1
67
P11
L02P_1
L06N_1
68
P12
L02N_1
L07P_1
70
P13
L03P_1
L07N_1
71
P14
L03N_1
P15
L04P_1
P16
L05P_1
P17
L05N_1
L03N_3
P34
P18
L06P_1
L03P_3
P33
P19
L06N_1
L02N_3
P32
P20
L07P_1
L02P_3
P31
P21
L07N_1
L01N_3
P30
P22
L02P_0
L01P_3
P29
P23
L02N_0
L06N_0
P28
P24
L03P_0
L06P_0
P27
P25
L03N_0
IO_L04N_1/RHCLK3
IO_L04N_3/LHCLK3
IO_L05P_1/RHCLK4
IO_L05P_3/LHCLK4
IO_L05N_1/RHCLK5
IO_L05N_3/LHCLK5
IO_L06P_1/RHCLK6
IO_L06P_3/LHCLK6
IO_L06N_1/RHCLK7
IO_L06N_3/LHCLK7
GND
GND
GND
GND
GND
GND
TCK_FPGA
1
TDO_FPGA
14 19 29 37 52 59 64 72 81 87 93
TMS_FPGA
7
GND
IO_L07N_3
GND
IO_L07N_1
GND
IO_L07P_3
GND
IO_L07P_1
2
3
+2V5
4
5
6
K3
P26
+3V3
1u
IC4
5
R10
IN
JP1
FLAG
EN
14
13
3
6
VCC
2
16V
2
UCAP
UVCC
24
44
AVCC
AVCC
PB1(PCINT1/SCLK)
PB2(PDI/PCINT2/MOSI)
PB3(PDO/PCINT3/MISO)
RESET
PB4(PCINT4/ADC11)
C10
2u2
6V3
CARD_DETECT
1
33
INIT_B
31
CLK_O
32
L1
30R@100MHz
PB5(PCINT5/OC1A/OC4B/ADC12)
PE6(INT6/AIN0)
PB6(PCINT6/OC1B/OC4B/ADC13)
PB7(PCINT7/OC0A/OC1C/RTS)
PE2(HWB)
PC6(PC3A/OC4A)
PD0(OC0B/SCL/INT0)
PC7(ICP3/CLK0/OC4)
PD1(SDA/INT1)
ATMEGA32U4
7
R1
1
3
22R
2
R2
3
4
22R
4
5
5
L2
30R@100MHz
34
VCC
PB0(SS/PCINT0)
RESET
1
C3
10u
6V3
D–
IC3
PD2(RXD1/INT2)
PD3(TXD1/INT3)
PD4(ICP1/ADC8)
VBUS
PD5(XCK1/CTS)
PD6(T1/OC4D/ADC9)
D–
PD7(T0/OC4D/ADC10)
D+
PF0(ADC0)
PF1(ADC1)
UGND
2
PF4(ADC4/TCK)
D+
42
GND
PF5(ADC5/TMS)
PF6(ADC6/TDO)
AREF
PF7(ADC7/TDI)
3
TPD2EUSB30ADRTR
GND
S2
15
S1
RESET
100n
10uH
R7
4k7
R9
C22
GND
XTAL1
23
XTAL2
17 X1
C21
C2
100n 16V
18p
8MHz
16
GND
GND
35
43
R6
4k7
R8
4k7
R5
4k7
100n
16V
IC1
GND
1
OPEN: EXTERNAL POWER
CLOSED: USB POWER
C23
1u
6V3
1
NCP380
LSN05AAT1G
4
4k7
OUT
C12
4k7
+5V_EXT
+5V_EXT
+2V5
6V3
L3
USB mini
NC
GND
2
C11
Figure 5.
Schematic diagram of the FPGA
development board. The complete
schematic takes up nearly an entire
page, but all of the components
fit on a PCB measuring just
65 x 25 mm.
EN
+1V2
5
GND
XC3S250-4E_VQ100
BANK 1
OUT
2
IP/VREF_1
IO_L04P_1/RHCLK2
IC5
TLV70212
DBV
TDI
FPGA_JTAG
K1
IN
41
IO_L07P_2/M0
PROG_B
DONE
INIT_B
38
IP_L05P_2/RDWR_B/GCLK0
IO_L06N_0/VREF_0
L01P_2
25
33
IO_L04N_2/D3/GCLK15
IO_L06P_0
24
32
IO_L03P_2/D7/GCLK12
IP_L04N_0/GCLK9
M1/SDA
27
IO_L02N_2/MOSI/CS_B
BANK 0
IP_L04P_0/GCLK8
1
CS
42
26
IO_L02P_2/DOUT/BUSY
IC2
IO_L03N_0/GCLK7
+5V_EXT
30
IP/VREF_2
TDI_FPGA
AVR_ISP
1
51
TMS_FPGA 75
+3V3
K4
99
P6
DET
POL
GND
L06P_0
MOSI
P4
G4
G3
G2
G1
GND
NC/DAT1
CS
P3
28 56 80
IO
GND
473093751
P2
6
IO_L01P_0
GND
MOLEX
MICRO_SD
91
P1
VCCO_1
+3V3
R3
82 97 55 73
VCCO_0
+3V3
This approach makes the work
flow very simple. After generating a configuration file with
the Xilinx ISE software, you can
use Windows Explorer to copy
the file to the MicroSD card,
since the board appears in the
Windows Explorer window as
a USB drive with its own drive
letter. After this you only have
to rename the file ‘config.bin’,
eject the drive from the PC, and
reset the board. The new configuration data is loaded when
the board starts up.
+2V5
C15
VCCO_0
The microcontroller must also
interpret and execute the SCSI
commands from the host system (PC) to allow the card to be
used with an operating system.
+3V3
AVR_JTAG
+1V2
8
CS
9
SCLK
10
MOSI
11
MISO
28
PROG-B
29
30
HSWAP
12
DONE
18
M0/SCL
19
M1/SDA
20
MISO_1
21
MOSI_1
25
M2
22
CCLK
26
27
41
40
39
TCK_AVR/ADC4
38
TMS_AVR/ADC5
37
TDO_AVR/ADC6
36
TDI_AVR/ADC7
C1
18p
120099 - 11
74874
Projects
Figure 6.
The PCB is built as a
four-layer board to allow
all of the interconnects to
be implemented in such a
small PCB area. The board is
supplied fully assembled.
its, the edge steepness and maximum source/
sink current per output can be set by the user.
PROG_B
IO_L01P_3
77 TCK
76 TDO
78
81
80
79
83 IO_L02P_0/GCLK4
82
75
Bank 0
Bank 1
24
25
IO_L08P_2/VS2
IO_L07N_1
IO_L07P_1
IO_L06N_1/RHCLK7
IO_L06P_1/RHCLK6
IO_L05N_1/RHCLK5
IO_L05P_1/RHCLK4/IRDY1
IO_L04P_1/RHCLK2
IO_L03N_1/RHCLK1
IO_L03P_1/RHCLK0
IO_L02N_1
IO_L02P_1
IO_L01N_1
IO_L01P_1
48
49
50
DONE
IO_L08N_2/VS1
IO_L09P_2/VS0
IO_L09N_2/CCLK
41
42
43
44
45
46
47
39
40
IO/M1
IO_L07P_2/M0
IO_L07N_2/DIN/D0
IP_L05N_2/M2/GCLK1
IO_L06P_2/D2/GCLK2
IO_L04P_2/D4/GCLK14
IO_L04N_2/D3/GCLK15
34
35
36
37
38
IO/D5
31
32
33
IO_L03P_2/D7/GCLK12
73
72
71
70
69
68
67
66
65
64
63
62
61
60
59
58
57
56
55
54
53
52
51
Bank 2
29
30
IO_L01P_2/CSO_B
IO_L01N_2/INIT_B
TMS
74
Bank 3
3
4
5
6
7
8
IO_L03P_3/LHCLK0
9
IO_L03N_3/LHCLK1 10
IO_L04P_3/LHCLK2 11
IO_L04N_3/LHCLK3/IRDY2 12
IP 13
14
IO_L05P_3/LHCLK4/TRDY2 15
IO_L05N_3/LHCLK5 16
IO_L06P_3/LHCLK6 17
IO_L06N_3/LHCLK7 18
19
20
21
IO_L07P_3 22
IO_L07N_3 23
87
86 IO_L03N_0/GCLK7
85 IO_L03P_0/GCLK6
84 IO_L02N_0/GCLK5
93
92
91 LED1 - IO_L05N_0/GCLK11
90 LED2 - IO_L05P_0/GCLK10
89
88
95 IO_L06N_0/VREF_0
94 IO_L06P_0
1
2
IO_L01N_3
IO_L02P_3
IO_L02N_3/VREF_3
26
27
28
Figure 7.
Pinout of the FPGA used on
the board. The orange and
green pins are brought out
to the connectors on the
board, while the blue pins
form the interface to the
microcontroller. The two
yellow pins are connected to
LEDs, and the black pins are
used for the JTAG interface,
which can be accessed via a
separate connector.
97
96
100 TDI
99 IO_L07N_0/HSWAP
98
Computation blocks
Since FPGA users often use logic blocks to perform computations, manufacturers have integrated ready-made computation blocks in their
FPGA products. This usually involves multipliers, but some manufacturers go a step further
GND 50
3.3V 49
3
SCLK
4
MOSI
5
RESET
6 GND
Figure 8.
The pins of the expansion
connectors. The orange and
green pins correspond to
the pins shown in Figure 7.
These connectors can
be used to program the
microcontroller. The pins of
the AVR JTAG port can also
be used as analog inputs.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
48
49
53
54
57
58
60
61
62
65
66
67
68
70
71
83
84
85
86
IO_L08N_2/VS1
IO_L09P_2/VS0
IO_L01P_1
IO_L01N_1
IO_L02P_1
IO_L02N_1
IO_L03P_1/RHCLK0
IO_L03N_1/RHCLK1
IO_L04P_1/RHCLK2
IO_L05P_1/RHCLK4/IRDY1
IO_L05N_1/RHCLK5
IO_L06P_1/RHCLK6
IO_L06N_1/RHCLK7
IO_L07P_1
IO_L07N_1
IO_L02P_0/GCLK4
IO_L02N_0/GCLK5
IO_L03P_0/GCLK6
IO_L03N_0/GCLK7
TCK_AVR/ADC4
TMS_AVR/ADC5
TDO_AVR/ADC6
TDI_AVR/ADC7
AVR JTAG
AVR ISP
1 3.3V
2
MISO
48
47
46
45
IO_L01P_2/CSO_B
IO_L07N_3
IO_L07P_3
IO_L06N_3/LHCLK7
IO_L06P_3/LHCLK6
IO_L05N_3/LHCLK5
IO_L05P_3/LHCLK4/TRDY2
IP
IO_L04N_3/LHCLK3/IRDY2
IO_L04P_3/LHCLK2
IO_L03N_3/LHCLK1
IO_L03P_3/LHCLK0
IO_L02N_3/VREF_3
IO_L02P_3
IO_L01N_3
IO_L01P_3
IO_L06N_0/VREF_0
IO_L06P_0
24
23
22
18
17
16
15
13
12
11
10
9
5
4
3
2
95
94
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
5V
and include DSP functions that can be used to
perform frequently used computations, such as
a + (b × c) → a (multiply-accumulate operation).
Memory blocks
Along with distributed RAM in the form of LUTs,
FPGAs have RAM blocks with a total capacity
that can reach the megabit range. Integration
of memory on the chip facilitates extremely high
data processing rates. It also allows complete
microcontroller systems to be implemented in
a single FPGA. RAM blocks can also be used as
first-in, first out (FIFO) data buffers by providing
them with two independent ports. These buffers
can be used to synchronise systems that operate
at different speeds, among other applications.
The word width of the memory is variable, so
blocks of various sizes (like 1-bit and 32-bit) can
be used intermingled.
Clock blocks
Although it is theoretically possible to implement
functions in asynchronous logic (i.e. without a
clock signal), this is usually not a good approach
for relatively complex systems. Differences in
signal path length in the circuit lead to time differences, with the result that signal edges that
were aligned at the point of departure are no
longer aligned at their destinations. This gives
rise to unintentional states in the circuit, which
lead to errors.
This solution to this problem is to sample the signals at regular intervals, which is analogous to
taking snapshots of the system state at specific
times. Although this slows down the system, it
keeps all the signal edges nicely aligned. This
synchronization is provided by clock signals and
flip-flops. However, clock signals are subject to
the same physical laws as other signals, so they
also experience delays as they propagate through
the chip. FPGA manufacturers have devised a
solution for this by integrating all sorts of delay
74874
and shift options in the clock blocks. The clock
signals can also be distributed over special clock
networks.
Another situation where using clock blocks is a
good idea is when you have subsystems operating
at different speeds (different clock domains). In
this situation the clock blocks can be configured
to generate different frequencies based on the
same input clock. The clock frequencies can be
very high, extending into the gigahertz range,
which can be very beneficial for the speed of
the circuit.
The fully assembled FPGA
development board is
available from Elektor
for approximately
£ 50 plus
shipping
charges.
Practical aspects
After this introductory description, it’s time to
turn our attention to practical aspects and to
start experimenting with a real FPGA. To this
end, Elektor designer Raymond Vermeulen has
developed a handy little FPGA development board
that eliminates one of the main hurdles of most
other FPGA development boards: the awkward
method for programming the configuration in the
FPGA. The software tools for configuring FPGAs
are rather complex, and in many cases you also
need an external JTAG programming device to
download the configuration data into the IC. Raymond came up with the idea of making the FPGA
board look like an intelligent USB stick to the host
PC, together with a MicroSD memory card on the
board. The configuration file can simply be copied to the memory card, just like any other file.
When the board is restarted, the file is read from
the ‘virtual USB stick’ and the data is loaded into
the FPGA. This elegantly eliminates the thorny
problem of developing specific drivers for specific
programming hardware.
Visit www.elektor.com/120099
nection, it’s a good idea to order the free software DVD from Xilinx (see Figure 9). It should
usually arrive within two weeks.
(120099)
Internet Links
[1] www.elektor.com/120099
[2] www.xilinx.com/support/download/index.htm
Coming up next
FPGA configuration is a complex subject, so our
aim in the next few instalments of this series is
to explain, as clearly as possible, how to create useful applications. If things go according
to plan, in next month’s issue of Elektor we will
first explain how to install the free Xilinx ISE
WebPACK software and how you should use it
to create a simple project that causes the LEDs
on the FPGA development board to blink. To fill
the time until the next instalment appears, we
recommend that you get a head start by downloading the Xilinx software [2]. The WebPACK
version is free, but it weighs in at a hefty 6 MB.
If you have a relatively low-speed Internet con-
Figure 9.
The free DVD from Xilinx,
which contains the ISE
WebPACK software and other
FPGA tools.
74874
Projects
Arduino
AC Grid Analyser
Frequency analysis
on a mini colour display
By Fidelis Theinert
(The Netherlands)
A fully fledged spectrum analyser on a basic Arduino board? In this article we’ll
show you how this is possible when the software is tailored to the available processing power. A standard Arduino can be turned into an AC line (‘mains’) supply spectrum analyser with the addition of a filter shield and a display shield. It
uses a Fast Fourier Transform to visualize the ‘pollution’ on the AC grid supply at
home or at the office.
74874
AC Grid Analyser
AC Line
50 / 60 Hz
Electrical
Isolation
Attenuation
Lowpass
10-bit ADC
Window
FFT
Serial
Output
Spectrum
Counter
Arduino
Frequency
Display
120546 - 11
A simple Arduino board is much more powerful
and versatile than many readers realize. In this
article we’ll use a practical example to show you
what the capabilities are of this small 8-bit microcontroller, but also what its limitations are. We
will also explain how the various components of
the microcontroller can be used efficiently and
which free development tools are required to
set up projects such as these. The software and
hardware are of a modular construction, which
makes it possible to use the individual modules
in other projects as well. The application was
tested successfully on an Arduino Duemillenova,
UNO R1, R2 and R3.
The circuit analyses the AC grid voltage using
a Fast Fourier Transform (FFT) and shows any
harmonics present on the display. This can then
be used to assess the quality of the supplied
(energy) signal. These higher harmonics cause
losses in machines and motors that are converted
into heat, but which you still have to pay for. Furthermore, the efficiency of switch mode power
supplies in PCs and other devices is compromised
by a supply signal that isn’t an ideal sinewave.
Fourier analysis
The Fast Fourier Transform is a mathematical
algorithm that converts a discrete signal from
the time domain into the frequency domain. The
improvement in execution time of the FFT compared with the ‘Discrete Fourier Transform’ (DFT)
can be quite substantial for a large number of
samples (N). With an FFT the Fourier transform
on a signal with N samples is split into two transforms with lengths of N/2.
This results in a much reduced execution time
since there are fewer calculations to be done, but
it does mean that the number of samples (N) has
to be a power of two (64, 128, 256, ... , 4096
...). In practice this is not a problem since the
Figure 1.
Block diagram for the
spectrum analyser.
length of the array can usually be freely chosen.
According to the Nyquist-Shannon sampling
theorem the bandwidth of the signal may not
be greater than half the sampling frequency. In
other words, the sampling frequency has to be at
least twice the value of the highest frequency we
want to investigate. With a sampling frequency
of 800 Hz you can therefore analyse a signal with
a bandwidth of 400 Hz, which makes it possible
to show the spectrum of the local AC grid supply
up to its sixth harmonic (60 Hz x 6 = 360 Hz),
or seventh (50 Hz / 350 Hz).
Hardware
The hardware consists of three boards: the
Arduino board [1], a filter shield developed by
the author and an LCD shield [2]. The two shields
can be mounted on the Arduino board (with the
LCD shield on top, of course), which results in a
compact and sturdy module without any loose
wires. Figure 1 shows a block diagram of the
complete setup.
When the Arduino has calculated the spectrum
it is also possible to send the result to a PC via
the serial port. The graph can then be plotted
using a terminal program (Putty, for example).
The transmission of the data requires a bit more
time since the whole graph is sent to the UART
of the PC at a rate of only 57,600 baud. This
feature will be particularly useful to those of you
who don’t have an LCD shield.
To make sure that the input signal doesn’t have
any frequency components above 400 Hz, a fourth
order Sallen-Key lowpass filter (or anti-aliasing
filter) with a bandwidth of 350 Hz is put in front
of the input (Figure 2). The two Butterworth
sections are made around a TS912 dual opamp.
This opamp has a rail-to-rail output and a wide
operating voltage range of 2.7 V to 16 V, which
74874
Projects
Power
RESET 1
3V3
2
5V
3
GND 4
GND 5
R7
47k
100n
C10
R5
3k9
R6
3k9
X1 2
8
2
IC1.A
1
R3
1k8
R4
1k8
Analog
6
IC1.B
7
C7
IC1 = TS912
100n
C1
C8
100n
22u
16V
1
100n
R2
C9
C4
100u
16V
100n
1k
C3
Figure 2.
Anti-aliasing filter (350 Hz
Butterworth lowpass filter).
JP1
5
4
R10
10k
6
680n
3
2u2
16V
VIN
R8
330R
R1
C5
1k
C2
LED1
A5
1
A4
2
A3
3
A2
4
A1
5
A0
6
JP3
120546 - 12
means it can be powered directly from the 5 V
supply voltage on the Arduino board.
The output signal from the filter goes directly
from pin 7 of IC1 to channel 5 of the ADC on
the microcontroller (an ATmega328P). The output of the opamp is also capacitively coupled to
connection A4 of the analog input connector of
the Arduino board, for measuring its frequency.
In Figure 3 you can see the shield board designed
FFT tricks
The Cooley-Tukey ‘butterfly’ algorithm implemented here is a
so-called ‘in-place transformation’; this means that the result
of the transformation is stored in the same buffer where the
original samples of the input signal were stored. The input
signal is therefore no longer available after the conversion.
The advantage of this is that the memory required for
the buffer is halved , which is extremely useful when the
microcontroller used (ATmega328) only has 2048 bytes of
memory available.
As was mentioned previously, the number of samples has
to be a power of 2. This condition is satisfied by the buffer
size of 256 (28) samples. The ADC has a resolution of 1024
levels, which means that two bytes are required to store
each sample, or 512 bytes for all of the samples. During
the calculations there is also a requirement for a buffer to
hold the imaginary part of the numbers, since the Fourier
transform is a conversion of complex numbers. This buffer
obviously needs to be the same size as the buffer for the real
part and therefore requires 512 bytes as well. In total we
therefore need 1024 bytes to store the values for the FFT,
which is half of the available memory.
In order to use the maths library of the GCC compiler it
would be useful if we could store the samples as ‘single
precision floating point’ variables instead of integers. (In an
FFT we don’t just have simple mathematical operations such
as addition and multiplication, but also sines, cosines, square
roots and exponentiation.) However, these require 4 bytes
each for storage, making the buffer 2048 bytes long, which is
as much as the available memory in the microcontroller, and
therefore too big for the chosen platform. One way round this
dilemma would be to halve the number of samples for the
FFT to 128, but this will result in a lower spectral resolution
and is therefore undesirable.
A different solution is therefore required if we want to keep
working with 256 samples. The real and imaginary parts
of the complex numbers are still stored as integer values
(2 bytes/sample) and converted into a ‘floating point’
variable before each mathematical operation and converted
back into integer format afterwards. The extra overhead
for these two conversions obviously makes the system a bit
slower, but it is acceptable. The rounding error introduced by
the conversion (1/65536) is a factor of 64 smaller than the
quantization error of the ADC (1/1024) and can therefore
be ignored (see the functions ‘FFT_Int2Float ()’ and ‘FFT_
Float2Int ()’ in the module fft_lib.c).
74874
AC Grid Analyser
for this filter. Note that there are some extra components on this board that aren’t used in this
application. The board layout is available from
the associated web page for this article [3].
The AC line voltage is electrically isolated using
a AC power adapter (an ‘old fashioned’ type with
a transformer). The output of the adapter is connected to terminal block X1. Since the filter has a
gain of one, a signal with an amplitude of 2 Vrms
(5 Vpp) is sufficient for the dynamic range of the
ADC in the ATmega. The output signal from the
transformer is not distorted in practice because
the transformer is effectively unloaded, as can
be seen in Figure 5 (the supply for the analyser
comes from a separate adapter or via the USB
connection).
Figure 3.
The PCB layout for the filter
shield.
This way it’s possible to measure all harmonics
in the domestic AC line supply fairly accurately.
Potentiometer R10 should be used to reduce the
output signal from the adapter to about 1.7 Vrms
at C10 when the input voltage is at its nominal
level, i.e. 115 V or 230 V. You can use a reference
multimeter to make a note of the line voltage
and then adjust R10 so that the voltage shown
on the display corresponds to that on the multimeter. We recommend that you use an AC power
adapter with an output voltage of less than 20 V.
In order to use the memory as efficiently as possible, the
samples from the ADC are initially stored in the buffer for
imaginary numbers. At that point in time this buffer isn’t
used by the FFT routine.
input
output
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
120546 - 17
Bit reversal algorithm
The samples are then normalized and scaled, with the results
stored in the buffer for real numbers.
The imaginary buffer can then be cleared and the window
function can be applied to the real part of the samples (this
window function is necessary in order to satisfy the boundary
conditions for the FFT).
An important aspect of the FFT implementation is the socalled ‘bit reversal’ algorithm, which is used for addressing
the samples in the buffers. At first this may look like a simple
operation (the bits of the value of a register have to be put in
reverse order, as shown in the figure above), but it isn’t very
easy to implement. Fast implementations use extra hardware
registers for this. Another alternative that is often used is a
table, but this requires a lot of memory and that is in limited
supply in a small microcontroller. The slowest method is to
shift all bits out of one register and shift them into another
register in reverse order. This requires a loop with a counter
and a total of 16 shift operations. A combination of these
methods is used here, which provides a good compromise
between memory usage and processing time. The byte is
split into two lots of 4 bits. Each of these 4-bit values is
reversed using a table and the results are then combined in
the right order into a byte again (see the function ‘fft_BitRev
()’ in module fft_lib.c). The resulting time saved is 3 µs (2 µs
instead of 5 µs) for each instance this function is called, but it
does require an extra 75 bytes for the code.
74874
Projects
Figure 4.
The three boards next to
each other.
Development Environment
We haven’t used the standard Arduino programming environment for the software development.
Instead, we’ve used the ‘GCC cross-compiler’ for
the AVR microcontroller series. The ‘cross-avr’
compiler can be installed under Linux from the
repositories of the distribution, along with the
associated ‘bin-utils’. For Windows you can install
the ‘WinAVR’ [4] package. For both operating
systems we’ve used version 4.3.3 of the GCC
compiler [5]. For uploading the compiled hex file
we’ve used the program ‘avrdude’. This program
is part of the WinAVR package for Windows, but
there is also a Linux version available. With both
versions you’ll get scripts that upload the executable to the Arduino. You will have to edit these
files so that you have the correct serial port for
communications with the Arduino and the path
to the executable on the PC.
We also need a program called ‘make’, which
compiles and links the source code of all modules with the help of a make-file. This program is
included with WinAVR as well, and is also available for Linux.
To edit the source code you can use your preferred editor. Eclipse with the CDT plugin is rec-
Table 1. Software modules
Name of
source code file
Name of associated
header file
Description of functionality
avrfft.c
(none)
Main source code file
drw_fft.c
drw_fft.h
High-level draw functions for graph display on LCD
fft_lib.c
fft_lib.h
Definitions and functions for the FFT calculations
freq_cnt.c
freq_cnt.h
Definitions and functions for data acquisition and
frequency measurement
lcd_driver.c
lcd_driver.h
Low-level functions and definitions for driving the LCD
menu.c
menu.h
Functions for reading the switches on the LCD shield
plt_fft.c
plt_fft.h
High-level functions for sending plots over the serial
port
ser_avr.c
ser_avr.h
Low-level functions for sending and receiving data
std_avr.c
std_avr.h
Commonly used standard definitions and functions
timer.h
Functions for timers and initialization of system
timing
timer_0.c
74874
AC Grid Analyser
Figure 5.
The AC grid voltage at
the primary side of the
transformer (blue) and the
voltage at the secondary
(yellow).
ommended, but Notepad++, Scite or just about
any other editor should be fine.
Software
The software has a modular construction and
consists of a number of source code files (see
Table 1).
Each C program begins with the function ‘main()’,
which can be found in the file avrfft.c. When the
program starts, it first initializes a number of
global system variables and the hardware with
the help of the associated init functions. Next, the
display on the LCD shield is cleared and the system timer is prepared for later use. The program
then comes to an endless loop, where the system
timer is set for a period of 2.5 s. This means that
a new cycle will start every 2.5 seconds.
All of the steps will always take place in the same
order during each cycle. A simplified flow chart
is shown in Figure 6.
Once the timer (timID) has indicated the start of
the next cycle, the 256 samples for the FFT will
be read in via the ADC with a sampling frequency
of 800 Hz. Next, the true effective value (TRMS)
of the signal voltage is calculated. In the next
step the frequency of the signal at pin A4 on connector ‘Analog In’ is measured using the built-in
comparator and Timer1 of the microcontroller.
The next steps (scaling the measured values and
applying the selected window function) prepare
the measured signal for the actual FFT calculations. At the end the result of the calculations is
sent to the display of the LCD shield to show the
spectrum of the signal.
Usage and display
The display on the LCD shield used has a resolution of 131 x 131 pixels, of which a window of 80
vertical and 96 horizontal pixels is used to plot
the spectrum. This results in a range of 0 Hz to
300 Hz (96 pixels x 3.125 Hz = 300 Hz) and 10
pixels per 6 dB vertical. The FFT routine calculates
the spectrum for 0 to 400 Hz, but frequencies
above 300 Hz aren’t shown, although they are
sent to the PC via the serial port. The measured
AC line voltage and frequency are shown below
the window, whereas the voltage is also shown
as an analog bar.
start
init
sample
To the left of the display on the LCD shield are
three buttons, which are used to configure the
spectrum analyser. Their functions have been
programmed as follows. When the analyser is
switched on it will immediately start its measurements and will show a logarithmic plot of the
measured spectrum on its display. With a press
of the top button the display changes to a frequency plot with a linear scale along the vertical
axis. Another press of this button changes the
display to the time domain (scope function) and
the first 96 scaled samples in the input buffer are
shown (see Figures 7 and 8 for the different
displays). Another press of the first button shows
the complete contents of the input buffer after
the window function has been applied. A fourth
press switches back to the frequency domain
with a logarithmic scale, as it was when the circuit was first switched on. The bottom button is
used to select the type of FFT window function.
When the analyser is switched on the default
window type is Hanning. Pressing the bottom
calculate
TRMS
frequency
measurement
scaling
window
function
FFT
display
120546 - 14
Figure 6.
Flow chart of the program.
74874
Projects
a
b
Figure 7.
Logarithmic (a) and linear
(b) plots of the frequency
domain shown on the
display.
button switches to a Blackman window and the
next press changes to a Hamming window. The
selected window function is always shown at the
bottom-right of the display: ‘N’ for Hanning, ‘B’
for Blackman and ‘M’ for Hamming.
The middle button turns the serial communication with a terminal on and off. When no data is
sent to the computer, the colour of the indicator for the window function turns from yellow to
green and back again after each spectrum has
been calculated. When the serial communication
is turned on the indicator turns from yellow to red.
Performance
Depending on the compiler settings, a calculation of the FFT can take up to 1 second in the
most unfavourable condition without optimization
(-O0). The size of the compiled program is then
about 26 KB. With optimization turned on (-O2)
the length of the executable shrinks to about
18 KB and the calculation of the FFT takes only
700 ms. The time taken to run through a complete
cycle of the program (measuring the frequency,
acquisition, calculating the TRMS, scaling, window function, calculating the FFT, scaling, plotting on the display) takes about 2100 ms with
optimization (-O2).
A cycle time of 2500 ms was chosen so that the
system has a predictable and constant response.
This is obviously when the transmission of data to
the serial port is turned off. A detailed description
of the ‘-O’ flags can be found in the documentation for the GCC compiler.
1372 bytes have been used of the available memory (RAM 2048 bytes), of which 1024 bytes are
for the FFT buffers. This is about 2/3 of the available memory. Only about 18 KB have been used
of the available program memory (ROM 32 KB).
Bearing in mind that the Arduino bootloader
needs about 2 KB, this leaves more than 10 KB
of ROM for possible enhancements.
Conclusions
The system described here is a fully functional
real-time FFT analyser for the AC grid supply,
which uses a 256-point floating-point FFT to calculate a new spectrum every 2.5 s and shows it
graphically on a display. All this is implemented
on an Arduino platform with only one third of its
program memory used.
This application shows how efficient and powerful
an 8-bit microcontroller can be when it is used
to perform advanced mathematical calculations
and display the results graphically, as well as
including a user-interface and communications
with a PC. But there are also limitations, such as
the available memory (which restricts the FFT to
256 points) and the time taken to perform the
calculations, although there is further room for
improvement.
For the development of this project only opensource tools were used and the Arduino platform
itself is completely open and freely available.
The software is modular and it is very easy to
use any of the modules in another project. The
software has been published under the GPL V3
74874
AC Grid Analyser
a
b
Figure 8.
Plots of the time domain
shown on the display (96
samples without a window
function (a) and 256
samples with a Hanning
window (b)).
license, which means you can use it in your own
projects if you want to. The conditions of the
GPL are published on the website for the ‘GNU
Operating System’ [6]. The full software package
and the board layout can be freely downloaded
from the associated web page on the Elektor
website [3].
Internet Links
[1] http://arduino.cc/en
[2] www.sparkfun.com/products/9363
[4] http://sourceforge.net/projects/winavr
[5] http://gcc.gnu.org/onlinedocs/gccint
[6] www.gnu.org/copyleft/gpl.html
Possible enhancements
Despite the extensive functionality that is already
implemented, it would be possible to add a calculation of the THD (total harmonic distortion)
to the analyser.
Another enhancement would be a speech analyser
that calculates the spectrum of a speech signal
with the help of an FFT and shows the result on
the display. This does require that the bandwidth
of the lowpass filter is adapted. The ADC in the
ATmega328 can still operate at its full resolution
of 10 bits at a sample frequency of 15 kHz, which
is more than enough for a speech signal with a
bandwidth of about 5 kHz.
The speed of the system can be improved if the
acquisition of new samples happens in the background via interrupts whilst the information is
being sent to the display. This results in a 0.3 s
(256 samples/800 Hz sample frequency) improvement. It is also possible to drive the display more
quickly using the SPI interface of the ATmega328.
Another enhancement is to have an elaborate
program on the PC to display the graphs, but
then we would no longer have a self-contained
FFT analyser on an Arduino board.
(120546)
Also read: Grid Frequency Meter, Elektor January
2012.
The author
After completing his studies in
electric engineering at Berlin
Technical University, Fidelis Theinert
worked for over 20 years at various
companies in Germany and The
Netherlands as a hardware and
software engineer and has also
taught at colleges. He currently
teaches electric engineering at
Haagse Hogeschool, Delft, The
Netherlands. His expertise is in the
field of embedded systems and in
particular in signal processing of
video as well as audio signals.
74874
Projects
Hyperactive LED Xmas Tree
With elaborate light show and daisy-chain capability
By Willem Tak
(Netherlands)
These days it has
become impossible
to imagine even Christmas
decorations without any electronics.
While in the past we usually had to
make do with a string of tiny, fragile
light bulbs, which would flash at the most, now
we can choose from many different types of LED lights with built-in light effects. But as a real electronics
enthusiast you can, of course, make one that is much better and more elaborate, such as this Xmas tree
which, with 56 LEDs can display an extensive light show lasting more than three-quarters of an hour.
It’s that time again to retrieve the Christmas
decorations from the attic and to start looking for
a (real or artificial) Christmas tree. Fortunately it
is now rare for such a tree to be decorated with
real candles. These were replaced long ago by
miniature light bulbs or even LEDs. This is also
true for other Christmas decorations, where LEDs
are becoming increasingly more common and are
controlled by an electronic circuit.
The author of the electronic Christmas tree
described here wanted to make a mini Christmas
tree which was a little bit more exclusive than the
standard products in the DIY stores or garden
centres. That resulted in a circuit which comprises
not much more than a microcontroller and 56
light emitting diodes. The LEDs are arranged on
a circuit board in the classic Christmas tree pattern, as you can see from the headline photo.
The intelligence is – as is usual with this type of
circuit — in the software! This ensures that the
microcontroller will light up the Christmas tree
in the most interesting patterns (take a look at
the video at [1]). It is even possible to join two
of these trees together, after which the patterns
that are produced will run back and forth between
the two trees. The result is an amazingly effec-
74874
LED Christmas Tree
tive eye-catcher when it is placed on the window
sill. And it contains more than just a few simple
effects – the cycle time after which the entire
performance repeats, amounts to no less than
40 minutes!
D56
D55
D54
D53
D52
D51
D50
D49
D48
D47
D46
D45
D44
D43
D42
D41
D40
D39
D38
D37
D36
D35
D34
D33
D32
D31
D30
D29
D28
D27
D26
D25
D24
D23
D22
D21
D20
D19
D18
D17
D16
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
C5
C4
C3
C2
C1
C0
C6
C7
A0
A1
A2
A3
8
7
6
5
4
3
2
1
K1
2
3
4
5
6
K1
+5V
7
21
2
27
R14
4k7
3
K2
1
C1
47u
2
26
25
24
VDD
RC7
IC1
RC6
RA0
RC5
RA1
RC4
RA2
RC3
RA3
RC2
RA4
RC1
RA5
RC0
PIC18F2685
RB1
RB6
RB5
RB2
RB4
RB3
RB7
VSS OSC1
8
9
OSC2
X1
C3
R13
R12
R11
R10
R9
R8...R13 =
680R; 820R; 1k
MCLR/VPP
RB0
1
18
17
16
15
14
13
12
11
22
23
R2
0R
R3
28
VSS
10
19
C2
K3
R4
0R
1
4k7
2
3
R5
4
5
330R
1
2
R8
C2
20
3
C0
C3
R1
4
R7
5
C1
6
R6
7
C4
C6
C7
A0
A1
A2
A3
A4
A5
B0
8
C5
K4
16 15 14 13 12 11 10 9
1
Because of the matrix configuration (each LED
is on for only 1/7th of the time) and the limited
current that can be supplied by the controller, the
LEDs do not light up extremely bright. But then
the circuit is not intended for use in environments
that are too bright (like a softly lit living room).
The author used wide viewing-angle LEDs purchased at SBL [2] and achieved a useful result
with those. Good results are therefore obtained
especially when you don’t use ordinary LEDs,
but bright LEDs with a high optical efficiency.
The outputs of the controller can be loaded with
a maximum of 25 mA. Due to the multiplexing that works out at about 3 mA per LED; in
the dark even that can be too much. The eight
resistors in the connections to port C determine
the current through each LED. Depending in the
desired brightness you can use resistors with a
value of 680 Ω, 820 Ω or 1 kΩ.
A4
16 15 14 13 12 11 10 9
4k7
The circuit itself (Figure 1) is very simple: the
LEDs are driven in an 8x7-matrix directly by the
microcontroller. The seven columns of eight LEDs
each are connected, one at a time, to the positive power supply voltage by pins A0 through A5
and B0. In addition, the rows of seven LEDs each
are pulled to ground via resistors by the outputs
of port C. The levels at the C outputs therefore
determine which LEDs from each column will light
up, while the A and B0 outputs take care of the
multiplexing of the columns.
B0
Seeing that the optical effects play an important
role here and it is not the intention that you will
see the same pattern again after only a short
time, the author chose a microcontroller with
a substantial amount of memory. This became
the type 18F2685-E/SP made by Microchip, a
microcontroller which is provided with 96 KB of
flash memory (that is, 96 KB of program space).
This memory is, incidentally, nearly entirely filled
with the present program, hence the very long
run time of over 50 minutes. The microcontroller
is clocked using a standard 24 MHz crystal (the
internal clock of 8 MHz turned out not to be fast
enough for some patterns).
A5
Little electronics, lots of memory
D1
24MHz
22p
22p
120634 - 11
Via the sync-connection (pins 22 and 23, brought
out to K3) it is possible to connect two electronic
Christmas trees together. Certain patterns will
then jump from one tree to the other. In order
to obtain this effect, pins 22 and 23 of the two
Christmas trees are connected to each other
with a crossover cable. The software determines
whether a tree is the left or the right version. The
l-version indicates (as can be expected) the left
tree and r indicates the right. The effects have
been written in such a way that the left tree
Figure 1.
It’s almost unworkable
to make it any simpler: a
microcontroller drives 56
matrix-connected LEDs
directly. All of the real work
sits in an extensive program
that takes care for the
control.
74874
Projects
K3
C2
C1
C3
5V
Figure 2.
The circuit board for the
microcontroller with a few
passive components. A
skilled electronics enthusiast
can also easily build this
on a piece of prototyping
board.
5
1
R1
X1
D1
R4
IC1
K1
R13
R5
R11
R3
R9 R8
1
R10
R12
R14
K2
R7 R6
K4
R2
16
1
should be positioned on the left, when viewed
from the front.
The status LED, connected to RB7 is not essential. When the power supply voltage is switched
on, or after a reset, the LED will rapidly flash a
few times. In this way the correct operation of
the PIC and its contents can be verified.
It is best to use a 5-VDC power adapter for the
power supply; any standard adapter is certainly
sufficient for two trees. When two trees are connected together, the power supply wires can run
together with the synchronization lines (all are
present at connector K3).
Figures 2 and 3 show the circuit boards designed
for this Christmas tree. These are available from
Elektor [1]. The construction is very easy, only a
few leaded components are used. For the connection between the microcontroller and the display
board it is best to use a short length of 16-way
ribbon cable.
The software for this circuit can be downloaded
free from the Elektor website [1]. There are separate versions for the left and right tree, keep that
in mind when programming. If you are going to
build only one tree then it doesn’t matter which
version you program into the PIC. The website
also contains a demo video made by the author
and the files for the PCB layout, for those who
would like to etch their own boards. If you are
not satisfied with the patterns offered by default,
then you can get stuck into the available source
code yourself. But with a program length of over
50 minutes, the pre-programmed light patterns
are not likely to bore for a while...
(120634)
Internet Links
Figure 3.
This is what the (double
sided) PCB with LEDs in
Christmas tree shape looks
like
[2] www.superbrightleds.com
COMPONENT LIST
C2,C3 = 27pF ceramic
Controller board
Resistors
Semiconductors
R1,R4,R14 = 4.7kΩ
R2,R3 = wire link
R5 = 330Ω (optional)
R6–R13 = 680Ω (820Ω, 1kΩ, see text)
Capacitors
C1 = 47µF 16V
D1 = LED, red, 3mm (optional)
IC1 = PIC18F2685-E/SP, programmed
K3 = 5-pin SIL pinheader
K4 = 16 pin-SIL pinheader (or short length of
16-way flat cable)
Optional: pushbutton for mode and reset
PCB # 120634-1 [1]
Miscellaneous
LED board
X1 = 24MHz quartz crystal
K1 = DC adapter socket (e.g. Lumberg type
CUI-PJ-031DH)
K2 = 2-pin SIL pinheader (optional)
D1–D56 = high-efficiency LED, 5mm
K1 = 16-pin SIL pinheader (see K4 controller board)
PCB # 120634-2 [1]
with every PCB Prototype order
EAGLE order button
pcb-pool.com/download-button
ff
20% o on your first PCB order
Free Phone UK: 0800 389 8560
[email protected]
All registered brands remain the registered trademarks of the respective manufacturer !
FREE Stencil
PCB-POOL® is a registered trademark of Beta LAYOUT GmbH
74874
www.pcb-pool.com
SPECIAL CHRISTMAS OFFER
3 ELEKTOR PRODUCTS FOR JUST £44.00
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Naamloos-7 1
06-11-12 14:20
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Projects
Embedded Linux
Made Easy (6)
Networks and servers
Linux’s modular structure makes it the
By
Benedikt Sauter [1]
ideal basis for all sorts of projects in
measurement and control. A custom
control system can be written in virtually any programming language you
choose, with the user interface served
up as a web page to a PC, tablet or
smartphone. In this article we will connect the Elektor Linux board to a typical
home network and then show how to
write our own server application. We
finish with a look at the Lua scripting
language.
Figure 1.
Overview of the system.
This series has already covered the most important aspects of Linux from the bootloader and
kernel to the installation of device drivers. However, we have not yet seen how everything can
be pulled together to construct a full-scale application, including for example the ‘control logic’
running in the background, a web interface for
configuration and operation, and a simple control
panel using a display and buttons.
Messaging between applications
Figure 1 shows a typical scenario. In the middle
we have the Linux system running the custom
application and a web server to allow control
from a wide range of devices using a browser.
We can also add a display and a couple of buttons, the display being controlled using a separate
program. The main application program is just
an ordinary process, running in the background
among many others. Such a program is known in
the Linux world as a ‘daemon’ or ‘service’. Once
a daemon has been started it continues to oper-
ate without further action on the part of the user.
There are various ways to implement the interface between the daemon and other programs:
such messaging between threads or processes is
called ‘inter-process communication’, or IPC. For
example, we can use pipes, FIFOs, shared memory, sockets, stdin and stdout (‘standard input’
and ‘standard output’), files, databases or any
number of auxiliary programs. Which approach
we choose depends on several factors. Are the
programs written in the same language? Does the
software have to be portable to other operating
systems? What data rate is required?
One widely-used approach is the classical network
‘socket’. Sockets have the significant advantage
that data and commands can be sent over a network if desired. It is very easy to send and receive
messages using sockets and suitable functions
and classes are available in a wide variety of different programming languages.
We have therefore chosen to use sockets as
the basis for communications between the pro-
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Embedded Linux made easy
grams described in this article. Since the web is
also based on standard sockets, we will also see
along the way how to access data on the internet directly. So, as a first step, we will equip the
Linux board with an internet connection.
Connecting to the Internet
We assume that you already have a router providing a connection to the internet and acting as
a gateway for the other devices on your network.
You will also need to connect a USB-to-LAN adaptor to the USB interface on the board and make
sure that the driver for it is loaded [2].
To integrate a new device into a network it needs
to know its IP address and other parameters
such as the gateway and DNS server addresses.
This can be done manually or by using DHCP
(‘Dynamic Host Configuration Protocol’). When
DHCP is used the router on the local network will
configure the Elektor Linux board automatically
(see Figure 2). To test whether an IP address
has been successfully assigned using DHCP, you
can use the ping command to see whether you
can establish contact with (for example) the web
server at www.elektor.com (see Figure 3).
If no DHCP server is available the network parameters have to be entered manually.
IP address
To set the board’s IP address, enter the command
ifconfig eth0 <ipaddress>
with the placeholder <ipaddress> replaced by
an unused IP address on your network. To check
that this has been successful, you can try pinging your router using the command
ping <routeraddress>
with the placeholder <routeraddress> replaced
by the IP address of your router.
Gateway address
In order to send packets over the Internet, the
board has to know the address of the router
which provides the gateway for network traffic.
This is configured using the command
route add default gw <routeraddress>
with the placeholder <routeraddress> again
replaced by the IP address of the router. To test
Figure 2.
Configuration of IP
addresses using DHCP.
Figure 3.
Testing access to a server
using the ‘ping’ command.
this step, you can try pinging any other computer
on the internet, for example by typing
ping 94.236.12.177
which will ping the Elektor web server. Assuming this is successful (that is, that no packets are
lost), we can proceed to the final step.
DNS server address
In order to navigate the internet using domain
names rather than IP addresses, each device
on the network needs access to a DNS server.
A DNS server can convert a string like ‘www.
elektor.com’ into its corresponding IP address.
To configure a DNS server for the Elektor Linux
board to use, it is necessary to edit the file ‘/
etc/resolv.conf’ (see Figure 4). Run the editor
by typing
nano /etc/resolv.conf
and look for the ‘nameserver’ entry in the file.
One option is to enter your router’s address here,
as most routers these days provide DNS services.
Alternatively, if you do not have a local DNS
server, it is possible to use one on the internet.
One that is easy to remember and ideal for testing
is run by Google on the IP address 8.8.8.8. Save
the file using control-O and then type control-X
to leave the editor.
You should now find that you can reach any server
on the internet using the ‘ping’ command followed by the name of the machine.
Writing your own server
Now that we have established a connection
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command prompt so that you can execute other
programs or commands.
The console will show
[1]+
Stopped
./a.out
and if you now type
fg
Figure 4.
Configuration of the DNS
server.
(where ‘fg’ means ‘foreground’) the console will
become blocked again. Suspend the program
again using control-Z and then type
Figure 5.
Downloading the file
‘server.c’.
bg
which will set the server program running again,
but this time in the background.
between the board and the internet, we can
directly download some example source code
for a server. The command ‘wget’, which will be
familiar to users of Linux on PCs, lets us transfer
any file we like from the internet onto our board.
Figure 5 shows the command being used to
download the server example code.
The server is written in the C programming language. For initial testing we will use the compiler
on the board; if you plan to develop the code to
any significant extent it is worth using the toolchain on the development PC.
Listing 1 shows the source code for the program. The basic function of the server is to listen
on port 5000. If it receives a connection on this
port from another device, it will reply with the
current time. The program could be extended to
include a command interpreter so that different
replies can be given or different actions carried
out in response to different commands sent by
the client.
To test the server we first need to compile it:
gcc server.c
When the compiler has finished, we start the
server by typing:
./a.out
The program will now apparently become unresponsive to the console (apart from control-C,
which exits the program). However, this is not
quite true: you can type control-Z, which suspends the server program and returns you to the
As we mentioned above, the example server code
sends the current time to any client that connects to it. We can try this out from the console
using the ‘telnet’ program, which takes as its parameters the IP address of the server and its port:
root@gnublin:~/c# telnet 127.0.0.1 5000
Tue Sep 27 21:34:49 2011
Connection closed by foreign host
To bring the server program back to the foreground (for example in order to terminate it),
simply type
fg
at the console.
Of course, you can equally well access the server
from a web browser. The server could also be
modified so that instead of simply returning the
time it carries out some other action, such as
turning an LED on and off. We showed how this
can be done in the previous instalment in the
series [2].
Remote access over the network
So far we have used ‘picocom’ or similar terminal
program to provide a console over the board’s
serial port. However, now that we have a network interface, we can run as many consoles as
we like over the network. This makes life much
easier, especially when developing applications.
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Listing 1: A simple server program.
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
<sys/socket.h>
<netinet/in.h>
<arpa/inet.h>
<stdio.h>
<stdlib.h>
<unistd.h>
<errno.h>
<string.h>
<sys/types.h>
<time.h>
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(5000);
bind(listenfd, (struct sockaddr*)&serv_addr,
sizeof(serv_addr));
listen(listenfd, 10);
while(1)
{
connfd = accept(listenfd, (struct sockaddr*)
NULL, NULL);
int main(int argc, char *argv[])
{
int listenfd = 0, connfd = 0;
struct sockaddr_in serv_addr;
ticks = time(NULL);
snprintf(sendBuff, sizeof(sendBuff),
“%.24s\r\n”, ctime(&ticks));
write(connfd, sendBuff, strlen(sendBuff));
char sendBuff[1025];
time_t ticks;
listenfd = socket(AF_INET, SOCK_STREAM, 0);
memset(&serv_addr, ‘0’, sizeof(serv_addr));
memset(sendBuff, ‘0’, sizeof(sendBuff));
For example, we can be editing the source code
in one console while simultaneously running and
testing the program in another.
We use SSH (the ‘secure shell’) to make the
connection to the Elektor Linux board over the
network. This console automatically provides an
encrypted communication channel to the board,
which has the advantage that other devices on the
network cannot intercept the information being
sent to and from the board.
SSH from Linux
Under Linux ‘ssh’ is one of the standard tools.
Type the following into the console on the host
computer:
ssh [email protected]
}
close(connfd);
sleep(1);
}
address of the board. Next click on ‘Open’ and you
will be asked to verify that the remote device’s
‘fingerprint’ (part of the SSH key for checking
the identity of the remote device). Click on ‘Yes’.
In response to the prompt ‘login as’ enter ‘root’.
Listing 2: A start-up script.
#!/bin/sh
if [ ! -d /var/log/lighttpd ]
then
mkdir /var/log/lighttpd
chown -R lighttpd:lighttpd /var/log/lighttpd
chmod 777 /var/log/lighttpd/
touch /var/log/lighttpd/error.log
fi
modprobe asix
udhcpc
with the IP address replaced by that of your Linux
board. When the connection has been established
with the board, type the word ‘yes’ (see Figure 6). Shortly the standard console will appear,
and you should feel at home!
SSH from Windows
Under Windows we can use the PuTTY program [3]. Figure 7 shows the program’s main
window, and again we have to enter the IP
echo 3 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio3/direction
chown lighttpd:lighttpd /sys/class/gpio/gpio3/value
chown lighttpd:lighttpd /dev/lpc313x_adc
echo 1 > /dev/lpc313x_adc
chmod 666 /var/log/lighttpd/error.log
/etc/init.d/lighttpd start
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Projects
ing games programs. The Lua interpreter is just
120 Kbyte in size but nevertheless implements
many of the most up-to-date constructs in programming. Accessing files (which in the Linux
world also means accessing devices and hardware
functions) is done using the commands io.open,
io.read, io.write and io.close. The author has written a Lua library for the Elektor Linux board providing easy access to the main hardware functions, including the GPIO and A/D converter.
Figure 6.
Accessing the board using
SSH under Linux.
The advantage of using an interpreted language
over a compiled language like C to build a simple control application is huge: you can easily
edit your programs directly on the board using
its built-in editor (nano or vi) and execute them
immediately.
Using our newly-configured internet connection
we can download the Lua example programs onto
the SD card as follows.
Figure 7.
Accessing the board using
SSH under Windows.
When you press enter you will be logged in to
the system.
Using the Lua scripting language for
simple applications
The previous example used the C programming
language. C is very commonly used, fast and popular. However, on a Linux system there are many
other languages available besides C: each has
its advantages and disadvantages and is aimed
at different applications.
One very flexible, fast and easy-to-use language is Lua. The language is interpreted, and
has become best known for its use in scriptFigure 8.
The "blink.lua" example
program.
mkdir lua
cd lua
wget http://www.gnublin.org/downloads/elektor.lua
wget http://www.gnublin.org/downloads/blink.lua
wget http://www.gnublin.org/downloads/button.lua
wget http://www.gnublin.org/downloads/adc_relay.lua
Figure 8 shows the listing of a simple Lua program that flashes the LED. First the Elektor library
has to be loaded. The LED is initialised with a
call to initLED() and then switched on and off
in an infinite loop.
The program can be run from the console as
follows:
lua blink.lua
The program ‘button.lua’ is a simple demonstration of how to control a relay using the IO15 button on the board. And Figure 9 shows the code
of the example program ‘adc_relay.lua’, which
reads voltage values from the A/D converter in an
infinite loop. If the reading is above the threshold
of 500 the relay contacts are closed; otherwise
they are opened. The program can be tested by
connecting a potentiometer to the analog input
as described in the previous instalment in this
series [2].
Figure 9.
The "adc_relay.lua" example
program.
There is plenty of information about Lua on the
internet [4] as well as some good books [5].
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Starting the web server and other
programs automatically
Figure 10.
Downloading the web server
start-up script.
It is rather inconvenient to have to restart a
server application (and perhaps also reconfigure
the hardware) manually each time the board is
rebooted. The solution to this is to include the
relevant commands in a start-up script. Listing 2
shows a suitable script to start up the web server
application from the previous instalments in this
series [2]. The file ‘start.sh’ can be downloaded
from the internet (see Figure 10).
In order to have this script run automatically
when the Linux system is booted, we can for
example add an entry in the file ‘/etc/rcS.d/
S55bootmisc.sh’ (the directory ‘/etc/rcS.d’ is
where the system start-up scripts are kept). First
open the file using an editor.
nano /etc/rcS.d/S55bootmisc.sh
Figure 11.
Accessing the board from an
iPhone.
LED on the board can be turned on and off by
touching the HTML button.
At the end of the file you will see the following
entries.
/bin/mkdir /var/run/sshd
/usr/sbin/sshd
After these add the line
/home/root/start.sh
and then save the file by pressing control-O and
exit the editor with control-X. To make sure that
the file ‘start.sh’ can be found it must be placed
in the directory ‘/root’. The file must also be
made executable by setting its ‘x’ flag as follows.
chmod +x /home/root/start.sh
At this point it is useful to note that the Gnublin
project community wiki [6] covers a very wide
range of hardware and software topics. It includes
guides to transmitting and receiving data over
the I2C, SPI and UART interfaces (including moving data to and from user space) and much more
besides.
We have invited readers to propose a topic for
the next instalment in this series: at the time of
going to press our poll was still open. We have
been eagerly awaiting your suggestions! We can
also announce that we are working on an expansion board that increases the range of interfaces
available: more on that also in the next issue.
(120578)
From now on whenever the board is booted it
will automatically establish a network connection
and start up the web server.
Access from a smartphone or tablet
In the previous instalment in the series we
showed how to access a demonstration web
application from a browser running on a PC. Of
course, such an application can equally well be
accessed from a smartphone or tablet, as long
as the network on which the Elektor Linux board
sits includes a WLAN access point to which the
mobile device can connect. Figure 11 shows the
HTML control interface running on an iPhone. The
Internet Links
[1] [email protected]
[3] www.putty.org
[4] www.lua.org
[5] www.lua.org/pil
[6] http://wiki.gnublin.org
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Arduino on Course (3b)
Part 3b:
Sensors talk to Android phones
By David Cuartielles
(Spain)
and
Last month we introduced a series of tools for working with Android and Arduino
Mega ADK. This month we go one step further in that process,
Andreas Goransson
showing you how to read sensors connected to Arduino, into the
(Sweden)
phone. With all development tools in place, running code in your
phone and making it talk to your Arduino will be very
easy, you can start by following the examples com
coming with the ADK libraries!
Android phone to test how things work. We have
made an extra effort in making sure the code
is compatible with the latest version of Android
OS, at the time of writing it was version 4.1,
code Jelly Bean.
Tip: download the code shown in this article
from Elektor’s website, as we are only showing
excerpts in the article.
Where we are now
Android devices are about
everywhere. There are many ways how to
approach the creation of applications for those.
In our case, we will continue exploring the use
of Processing [1] as a way to write, compile and
upload code for/to Android phones.
Materials
Continuing with the experiments performed last
month, the materials for making the upcoming
experiment are going to be:
• Arduino Mega ADK board or Arduino Uno
board with USB Host Shield
• Android phone with Android OS 2.3.4 or
newer (the newer OS the better)
• USB cable and microUSB cable
• TinkerKit Shield (this is optional, you could
use a breadboard and jumper wires)
• TinkerKit Modules: Potentiometer and Pushbutton (also optional)
Note: in this article you really need to have an
At this point you have a certain understanding of
Google’s Accessory mode and how accessories
tell Android devices to boot a certain app when
connecting. You are familiar with Processing, the
Java learning tool, and have created and uploaded
small apps to your phone or tablet.
The next step is moving into creating new apps
that will take advantage of the connectivity
between Arduino — as an accessory — and your
Android.
The USB Host Library
The Android Open Accessory Protocol (AOAP) is
what determines how your Android device and
your Arduino board can talk to each other. The
Arduino board is technically a USB Host, while the
phone becomes a USB Client. Android devices,
like most of the state-of-the-art devices out there,
carry a peripheral that performs the so-called
USB On The Go functionality. According to it, the
same USB connector (currently micro USB connector) can become a USB client (like a mouse
or a keyboard) or a USB Host (like the one in
your Personal Computer).
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Arduino On Course
The AOAP establishes that accessories act as
hosts while the Android devices act as clients.
This allows the host feed the client with electricity (you Arduino board will be re-charging your
phone once plugged), among other features.
To establish the communication between the two,
you saw in the previous article that you need to
run the USB Host library as part of your Arduino
code. You could check one of the examples to
the library just to confirm you have it installed.
Note: use the menu to navigate through: “File
/ Examples / USB Host”, if you didn’t find those
examples there, it would mean that you hadn’t
installed the USB Host library in Arduino. Check
the downloads for this article [3] and install it;
you are going to need it. Figure 1 shows the
hardware involved.
Figure 1.
Arduino Mega ADK with
Tinker Kit Shield and phone.
Experimental setup:
the processing side
Let’s first look into the software you need to program you Android applications:
• Android SDK with all the updates up to the
latest version of the APIs
• Processing 2.0b3 or newer (if you read the
first article, you will see we have updated to
the latest version, you should do the same
at this point)
• The Arduino ADK Tool for Processing
• The Arduino ADK USB Library for Processing
The last item in that list is what you will be missing if you experimented with the previous article
in the series. That one was omitted intentionally
back then.
You need the complementary library to USB Host
on the Processing side to make sure you can get
your board to talk to your phone. We call that
library “Arduino ADK USB”. The following section
explains how to install it; Figure 2 shows the
hardware side of things.
Installing the Arduino ADK USB Library
for Android
Inside the download archive for this article you
will find a folder named “Processing”
which will have a subfolder called ‘libraries’. You
should copy the contents of that folder inside your
Processing libraries folder. The latter is located
inside your Processing sketchbook folder, usually stored at ‘My Documents/Processing’ in Win-
Figure 2.
Arduino Mega ADK
connected to a PC and to a
phone.
dows computers or “Documents/Processing” in
Mac and Linux.
This library comes with four examples. We recommend you start you accessories from one of
those examples, as it will make your life much
easier. Let’s start by trying out the example called
‘digitalWrite’. In this case you will be connecting your Arduino board to the phone and when
touching the screen, an LED connected to your
board will go on. If you stop touching the screen,
the LED will go off.
DigitalWrite
Each example has two parts. The first one runs
on the Arduino board, it handles the communication to and from the phone, while performing actions on the other pins on the board. The
second part is code to be compiled in Processing and that will run inside the Android device.
This app will be reading and writing data to the
phone’s cable connection as well as performing
some actions on the screen or reading any of the
phone’s sensors like camera, accelerometer, etc.
Let’s first analyse the Arduino code, open your
Arduino IDE and type in the code at Listing 1.
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Listing 1. DigitalWrite example from the Arduino’s USB Host library.
#include <AndroidAccessory.h>
// accessory descriptor. It’s how Arduino identifies itself to Android
char accessoryName[] = “DigitalWrite”; // your Arduino board
char companyName[] = “Arduino SA”;
// led variables
int ledPin = 10;
// counters
long timer = millis();
// initialize the accessory:
AndroidAccessory usb(companyName, accessoryName);
void setup() {
// start the connection to the device over the USB host:
usb.begin();
// configure the LED pin as output
Remember to upload it to the board once you
are done!
This code example will be listening to the USB
port. Once the phone connects to the Arduino
board, the usb.isConnected() function will
return an affirmative answer. When the phone
starts sending data, usb.available() will return
a value different from zero that Arduino will then
read and store in the variable val. Something
very similar to what’s pictured in Figure 3 should
happen at your place too.
Listing 2. Processing sketch that will detect screen touches.
import cc.arduino.*;
// create the ADK object
ArduinoAdkUsb arduino;
void setup() {
// Lock PORTRAIT view
orientation( PORTRAIT );
// initialize the ADK object
arduino = new ArduinoAdkUsb( this );
if ( arduino.list() != null )
arduino.connect( arduino.list()[0] );
}
void draw() {
// Draws a filled rect based on arduino connection state
connected( arduino.isConnected() );
}
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Arduino On Course
pinMode(ledPin, OUTPUT);
}
void loop() {
// print to USB 10 times per second
if(millis()-timer>100) {
if (usb.isConnected()) { // is the USB connection open?
if (usb.available() > 0) { // is there data?
char val = usb.read();
// ‘a’ turns the LED on, ‘b’ off
if( val == ‘a’ )
digitalWrite( ledPin, HIGH );
else if( val == ‘b’ )
digitalWrite( ledPin, LOW );
}
timer = millis();
}
}
}
On the Processing side you will need to write a
program that will check for the event of someone touching the screen. If there is a connection over the cable, the phone will then send ‘a’
to indicate someone just started touching the
screen. It will send ‘b’ to indicate the finger was
just lifted. We are detecting the events ‘start’
and ‘stop touching’ as we don’t want to flood
the communication port.
Open your Processing IDE and search for the
adk_digitalWrite example. You will find it at
the menu ‘Examples / Contributed Libraries /
public boolean surfaceTouchEvent(MotionEvent event) {
if ( arduino.isConnected() ) {
if ( event.getAction() == MotionEvent.ACTION_DOWN )
arduino.write(‘a’);
else if ( event.getAction() == MotionEvent.ACTION_UP )
arduino.write(‘b’);
}
// if you want the variables for motionX/motionY,
// mouseX/mouseY etc.
// to work properly, you’ll need to call
// super.surfaceTouchEvent().
return super.surfaceTouchEvent(event);
}
[…]
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ArduinoADKUsb’ if you installed the library properly, see Listing 2.
The code in Listing 2 is mostly self-explanatory. One part you might find a little upsetting
is the method definition surfaceTouchEvent
(Motion-Event event). Java is a very powerful
programming language and in this case it allows
overriding some of the existing callback methods.
Whenever you touch the Android’s screen, the
system is configured to call that specific function (surfaceTouchEvent(MotionEvent event)).
If you override it in your program (basically, if
you rewrite it) you can make it do whatever you
want to.
In this case, we detect two of the many system
events: MotionEvent.ACTION_DOWN (the equivalent to start pressing the screen) to send ‘a’ to
Arduino and MotionEvent.ACTION_UP (the same
for stop pressing the screen) to send ‘b’.
A bit more fun
Once you have got the first example to run…
why not building something a little more fun?
The Internet is packed with cats, that’s why we
decided to create the Elektor_Miau application
last month. We wanted to make a fun comment
and, at the same time, show you that it is possible to start making things more appealing than
the classic “Hello World” example when learning
programming.
This month we want to build upon the story and
encourage you to learn how to make small animations using Processing. You can look for any
animated GIF on the internet and use it to replicate what you will see in this example. The
only condition is that you need the animated
gif exported as frames. You should name them
in the following way: s00.gif, s01.gif, s02.gif …
You are of course welcome to use the same image
we are using for our article. We got an illustrator to draw for us a small rabbit appearing out
of a hat. The goal of this example is making a
small interactive game where you will use sensors (a button and a potentiometer) to interact
with the small rabbit on the phone’s screen, like
in Figure 4.
This time it will best to start looking at the code
to be running inside the phone. The first step is
building an animation inside Processing. If you
are versed in Android, you can try porting the
GIFdecoder library we used last month to play
animated GIFs inside your Android app. As we
want to keep the programming simple to understand, the way we recommend you animate your
Rabbit is very simple: you should make an array
of images designed to contain the frames you
want to be part of the animation. This concept is
based in the Processing example Animated Sprite
by James Paterson [2], see Listing 3 at [3].
Note: Listing 3 is not showing the Animation class
that will open all the images named s00.gif, s01.
gif, etc. We recommend you check the full code
listing coming with the example Elektor_Simple_Animation. You will also see a folder called
‘data’ inside the Processing sketch folder containing all the images that are part of the animation
(54 in total).
The ultimate setup
Next up, we’ll modify the example to include the
library handling the USB communication. We recommend you merge the previous code with the
adk_analogRead example. The result will look
like the code in Listing 4 you can find at [3].
There are a couple of things in the example that
need to be highlighted. First there is an array
called delays[i]. It’s responsible for controlling the time each frame will be displayed in the
animation. Every time you load a new frame,
you also change the timer length in the condition millis()- timer > delays[index]. You
are welcome to experiment with the numbers in
that array to see how it affects the animation.
Remember there have to be as many numbers
as frames in the animation.
Also there is a keyFrames[i] array that holds a
list of frames in the animation that will be expecting an action from the user for the movie to continue. In this case we are going to detect button
presses. The animation will stop at those frames
until the user presses the button attached to the
TinkerKit Shield as seen in Figure 5.
If you look at the line checking how many
bytes arrived from the Arduino board, we check
arduino.available() >= 3 to see whether
we got 3 bytes. The information is encoded as
follows:
• Byte 0: has to be 255, it’s a marker we use
to distinguish when the block starts;
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Arduino On Course
• Byte 1: is the potentiometer’s value; range
0 to 254;
• Byte 2: comes from the button; it will be
either 0 or 1.
The potentiometer’s value will be used to change
the screen background colour, while the button
will trigger the next sequence of the animation.
Note: use the Arduino ADK Usb tool (menu ‘Tools
/ Arduino ADK’ in your Processing IDE) to upload
this program from to your phone. A dialog window will pop up. In the text field labelled “model”,
enter the name of the app you call inside Arduino’s IDE. The last parameter is used to select
the version of the SDK for your accessory type.
If your phone or tablet runs Android 3.0 or later,
you should check SDK v12; SDK v10 is only for
those devices running Android 2.3.4. In the unfortunate case your Android device was running OS
version 2.3.3 or earlier, you wouldn’t be able of
using the Accessory mode.
Figure 3.
The LED is on when touching
the screen.
Figure 4.
A couple of frames of our
rabbit movie.
Finally, the Arduino code is practically a repeat of
the adk_analogRead example adding the extra
marker byte, limiting the analog reading to 254
and adding the button. The loop for that program is found in Listing 5 at [3]. Please check
the full program inside the documentation you
can get from Elektor’s website [1], in the folder
“Arduino / code”.
Closing words
With this article we finish our introduction to
Android and how it connects to Arduino. You
should be ready to create new projects, build
robots where your phone can be the intelligence,
or integrate sensors that aren’t coming with your
Android device. If you make any cool projects
using any of our code don’t hesitate to drop us
a line at [email protected], we will be happy to
let the rest of the community know about them.
(120573)
Internet Links & References
[1] Processing Project: http://processing.org
[2] Animations using multiple images with Processing: http://processing.org/learning/topics/sequential.html
Figure 5.
Button and potentiometer
on top of the TinkerKit
Shield.
Acknowledgements
The Arduino design team expresses its
thanks to the team at Circuits@Home for
their first work on the USB Host Library for
Arduino and Philip Lindsay for his work on
debugging the initial collection of official
Arduino Libraries for Android. Also to
Rodrigo Calvo who helped unveiling how to
improve the USB Host library to work with
Android 4.1 devices. And Laura Balboa for
her illustration job.
74874
Projects
Electronics for Starters
(10)
Radio Frequency (RF)
By Burkhard Kainka
(Germany)
It all started with high frequencies: radio technology was the driving force of
electronics. At first there were electron tubes and AM radio, later followed by VHF
and FM. Now we work with semiconductor devices, and the frequencies just keep
on rising. Nevertheless, RF projects for the medium- and short-wave bands are
still extremely interesting, especially for starters.
Building you own radio is still a good way to
get started in electronics. However, your first
radio project should be very simple, with no
special components, and as foolproof as possible.
The wideband regenerative receiver shown in
+9V
10k
ANT
AF
1M
10u
10n
10u
BC547B
GND
10k
32
47R
antenna, 3 ft.
10k
Figure 1.
A wideband regenerative
receiver.
1M
10u
Figure 2.
A regenerative receiver
with higher gain and better
selectivity.
1V5
Figure 1 fits the bill. A regenerative receiver is a
circuit that amplifies HF signals and demodulates
them at the same time. With this extremely
simple receiver you can listen to everything on the
ether, whether it be a medium-wave broadcasting
station or a very distant short-wave transmitter
– and of course all possible types of HF noise
in the near vicinity. The only prerequisite is a
sufficiently long wire antenna. Around 30 feet
of wire in the open air is ideal, but even shorter
antennas can still yield good results. You also
need an earth connection. A sensitive headset
can be connected to the audio output, or better
yet, a loudspeaker amplifier.
The wideband regenerative receiver picks up
everything at the same time. You will usually
hear several transmitter signals, although most
of the time one of them will be distinctly louder.
The frequency range of the receiver is partially
determined by the coil you use. If you wish, you
can also use a fixed inductor. For medium wave
reception the coil should have an inductance of
around 300 µH, and for short wave reception
approximately 10 µH, or as little as 3 µH if you
want to listen to the higher-frequency bands in
the 15 to 17 MHz range. A DIY coil for medium
wave reception could consist of 100 turns on a
ferrite rod. For short wave reception a coil with
10 to 30 turns and a diameter of 10 mm, without
a ferrite core, is enough. However, the results
also depend on the antenna.
22n
3x BC547B
It’s a good idea to try several types of coil or
inductor. A wide variety of stations can be heard,
74874
depending on the receiving site, the time of day
and the coil that you use. For example, you may
sometimes be able to listen to Radio China with
this simple receiver, since the range is especially
great in the higher-frequency short wave bands.
If you take a good look at the circuit, you will see
that it consists of a single amplifier stage. This
means that the high frequency signal from the
antenna is amplified. With a truly ideal amplifier
you wouldn’t be able to hear anything, since
the signal frequencies are far above the audible
range. The reason that you do hear something
is that the transistor has a non-linear input
characteristic. As a result, the positive half-waves
of the HF signal increase the collector current
more than the negative half-waves reduce the
current. This means that the average current
varies according to the amplitude of the HF input
signal. And because the transmitter modulates
the amplitude of the HF signal at the frequency
of the audio signal, the demodulated audio signal
appears at the output of the receiver.
The capacitors in the circuit are also important.
The relatively large capacitor at the input shorts
audio signals on the base of the transistor to
ground via the input coil, so that only HF signals
are present at the base. The current in the
collector circuit consists of a combination of the
amplified HF signal and the audio signal. The
10 nF capacitor at the output shorts the HF signal
to ground, leaving the audible AC signal in the
audio range. The end result is a simple, low-cost
receiver with fairly good sensitivity.
Figure 2 shows a simple radio with the same sort
of receiver stage, but with more gain and better
selectivity. It has a tunable resonant circuit at the
input. Depending on the coil characteristics, this
radio can receive signals over a range extending
from the long-wave band up to the upper shortwave region. The receiver coil is tapped at
approximately 10% of its length. This keeps the
damping factor of the resonant circuit relatively
low, which means it has a good Q (quality) factor
(see the ‘Resonant Circuits’ inset). This tuned
circuit allows a specific broadcast signal to be
selected. With a total of three transistors and a
supply voltage of just 1.5 V, this circuit works
well as a headphone receiver. Incidentally, this
circuit has a certain similarity to the TAPIR HF
Sniffer published in the July & August 2012 issue
of Elektor, which also has three transistors but
operates as a wideband regenerative receiver.
Resonant Circuits
If you combine an inductance (L) with
a capacitance (C) you get a resonant
circuit. In a manner similar to mechanical
energy in a pendulum, electrical energy
L
R
can flow back and forth between the
C
inductor and the capacitor at a specific
frequency (f), which is called the
resonant frequency. A resonant circuit
oscillates after being excited by any short
pulse of electricity. An ideal resonant
circuit would have no losses and would
therefore oscillate forever after being
excited.
However, in practice the oscillation is damped because energy is
dissipated in the form of heat due to the resistance of coil winding,
magnetic losses in the core of the inductor, and electromagnetic
radiation. For the sake of simplicity all of these losses can be
collectively represented by a resistance R in parallel with the circuit.
The resonant frequency f is given by the formula:
f = 1 / (2 p √ LC)
A quality factor (Q factor) can be specified for every resonant circuit.
Q is determined by the ratio of the parallel damping resistance R to
the inductive impedance ZL = 2 √ fL or the capacitive impedance
ZC = 1 / (2 √ fC) at the resonant frequency, at which the impedance is
resistive:
Q = R / ZL or Q = R / ZC
If a resonant circuit is excited by a variable-frequency signal from an AC
signal generator with high internal impedance, the voltage across the
resonant circuit is the highest at the resonant frequency. The amplitude
of the voltage at the resonant frequency is directly proportional to
the Q factor, or in other words, the lower the damping due to energy
dissipation of any form, the higher the resonant voltage. At either side
of the resonant frequency it is possible to find points on the resonance
curve where the voltage is reduced by a factor of 0.707 (1 / √2), or
3 dB down from the maximum. The frequency difference between these
two points is designated the bandwidth b of the resonant circuit. The
relationship between the resonant frequency f, the bandwidth b and the
Q factor of the circuit is given by the formula b = f / Q.
With careful coil construction it is usually possible to attain Q factors
up 100 or so. However, resonant circuits are also damped by the
connected circuit or connected antenna. This damping can be countered
by using a small coupling winding, a coil tap or a suitable capacitor to
achieve loose coupling. If the resonant circuit is connected directly to a
gain stage, this stage should have high internal impedance to keep the
damping small.
74874
Projects
Generating HF signals
800Hz
22k
12V
68n
100p
800kHz
Figure 3.
A tuned ‘spark gap’
transmitter.
BC548C
+9V
100k
20p
500p
HF
10p
BC547B
Figure 4.
A sine wave oscillator with
inductive coupling.
GND
1V5
1k
2x
BC547B
Figure 5.
An oscillator for use with
low supply voltage.
+9V
1k
100k
100n
RF
Figure 6.
An oscillator with a
tapped coil.
You don’t really need a high-power transmitter
suitable for a pirate radio station, but a signal
generator that produces just a wee bit of RF
power can come in handy now and then, if
only for testing your own receivers. Figure 3
shows a tiny transmitter circuit that works on
the same principle as the old-fashioned sparkgap transmitter. In this case the periodic pulses
at a frequency of around 800 kHz result from
switching an NPN transistor in an astable
multivibrator circuit (see instalment #7 of this
series in the September 2012 issue of Elektor
[2]). Each steep pulse edge excites oscillations
in the resonant circuit, which then quickly decay
as damped oscillations. The transmit frequency is
determined by the resonant circuit. For example,
if you use a ferrite rod antenna from an old
radio, the frequency will be somewhere in the
medium wave band, such as 800 kHz. You will
hear a humming sound if you hold a radio close
to the ferrite rod. All you need now for a fullfledged transmitter is a Morse key. The shipboard
transmitters of days gone by worked in a similar
manner, but with considerably more power and
at much lower frequencies.
LC oscillators
22p
BC547B
The world’s first transmitter was a spark-gap
device. To see how it works, all you need is an
ordinary light switch. When you flip the switch,
you can hear a bit of static on the radio — at least
if you’re listening to the medium wave band and
you aren’t receiving a signal from a strong AM
transmitter. A pulse waveform with steep edges
always has signal components in the RF range. In
fact, in many places switch-mode power supplies
and other electrical devices are a major source
of radio interference, especially in the medium
wave band. This means that the difficulty is not
generating RF signals, but instead preventing the
radiation of undesirable RF signals.
GND
Spark-gap oscillators could only transmit damped
oscillations. The first real progress came with the
invention of electron tubes, which were able to
generate undamped oscillations. In the previous
instalment of this series, which dealt with sine
wave oscillators [3], we described what you need
for this: enough gain and suitable feedback.
The grandfather of all RF oscillators is the
Armstrong or Meissner oscillator, in which a
74874
This problem does not occur with the oscillator
shown in Figure 5, since it has automatic
amplitude stabilization. Furthermore, this circuit
only needs a simple coil without a coupling
winding or a tap, and it the coil doesn’t even need
to have an especially high Q factor, thanks to the
high gain. This circuit is therefore a good choice
for DIY construction, and it always oscillates
reliably. Here the feedback is provided by a pair
of transistors. Both transistors also operate at
a very low voltage (approximately 0.6 V). The
circuit can operate with a supply voltage as low
as 1 V and can also operate with very low current
consumption. This can be advantageous for some
applications.
The basic circuit can operate over a wide
frequency range extending from audio to UHF,
depending on the resonant circuit, making it ideal
for building small test oscillators or the like with
little effort or expense. However, it does have
a drawback: the internal capacitances of the
transistors affect the frequency, and they also
depend on the operating voltage. This means
that although the circuit is very simple, it’s not
exactly a shining example of frequency stability.
An AM signal generator
that couples directly
to the ferrite rod of
the receiver. The
signal generator
can also be used for
comparative sensitive
measurements by
testing how far away
from the generator
the signal can still
be heard. A good
receiver can receive
a clear signal at
distances up to 3
feet.
The source code can
be downloaded from
the web page for this
article [4].
120R
Anyone who designs
+5V
or builds radio
receivers can make
good use of a small
100n
AM signal generator.
ANT.
With a suitable
VCC
PB2
PB1
signal waveform,
ATtiny13
you don’t even
RES
PB3
PB4
GND
need to be able to
adjust the frequency.
This works if the
generator operates
at an adequately
100n
low frequency and
generates enough
harmonics. The
ATtiny13 AM signal generator described here produces short pulses at a
frequency of 70 kHz. This results in strong harmonics covering the entire
long-wave and medium-wave spectrum. The pulse train is also briefly
interrupted at regular intervals to produce amplitude modulation at a
frequency of 750 Hz. A radio can therefore receive an AM test signal at
70 kHz, 140 kHz, 210 kHz, etc. and demodulate it to produce a humming
tone.
A wire loop with a
diameter of about
'ATtiny13 AM Generator
4 inches (10 cm) or
$regfile = "attiny13.dat"
so makes a suitable
$crystal = 1200000
antenna. It generates
$hwstack = 8
an AC magnetic field
120R
coupling coil provides feedback with the right
phase (Figure 4). The first radio transmitters
were also built this way: take a tube and a
resonant circuit and add a bit of feedback, and
you’ve got an RF power oscillator. Modulation
was handled very simply by fitting a carbon
microphone in the antenna lead (!).
The circuit diagram in Figure 4 shows a singletransistor Armstrong oscillator. It’s not difficult to
get this circuit to oscillate. If you have problems,
the phase may be wrong, in which case all you
need to do is to reverse leads of the coupling coil.
The frequency of this simple oscillator can
be adjusted with the variable capacitor. The
amplitude depends on a lot of factors, including
the coil damping, the feedback winding, and
the coupling capacitor. Sometimes it takes a
bit of experimentation before you get stable
oscillation, since this circuit has a peculiar
problem: it is prone to intermittent oscillation
if the amplitude is too great. This is caused
by rectification of the HF signal by the base–
emitter diode, which drives the base negative
until the transistor is cut off and oscillation
suddenly stops. After a few microseconds the
base resistor restores the normal operating
point and the cycle starts over again.
$swstack = 4
$framesize = 4
Config Portb = Output
Dim N As Byte
Do
For N = 1 To 50
'70 kHz
Portb = 255
Portb = 0
Next N
For N = 1 To 50
'AM 750 Hz
nop
nop
Next N
Loop
End
74874
Projects
100k
+9V
22p
BC547B
100n
RF
100p
1k
10n
220p
Figure 7.
An oscillator with a
capacitive voltage divider.
GND
However, direct coupling to the resonant circuit
affects the frequency in this circuit as well,
since the voltage divider capacitances vary with
the operating voltage. This simple oscillator
also highlights a stability problem that may be
encountered with amplification stages using a
common-collector configuration. Although your
intention may simply be to use an emitter follower
as an impedance converter, it can inadvertently
turn out to be an oscillator. Whether the circuit
acts as an amplifier or as an oscillator depends
on several factors, including the operating point
and the damping of the resonant circuit.
Crystal oscillators
If you need a really stable frequency, you should
use a crystal oscillator. Quartz crystals have
essentially the same characteristics as a resonant
circuit with an extremely high Q factor. They
can therefore be used to build relatively simple
oscillators with good frequency stability. A typical
circuit is shown in Figure 9.
1k
BC558C
Figure 8.
A DC coupled oscillator
in common-collector
configuration.
1k
+9V
RF
100p
22p
100k
6MHz
BC547B
33p
GND
Figure 9.
A crystal oscillator.
Maybe you can think of some way to remedy this
— such as wireless battery voltage monitoring?
Another way to obtain the right phase relationship
in an oscillator is to use a tapped coil, as
illustrated in Figure 6. Alternatively you can
use a capacitive voltage divider (Figure 7). The
circuit can be simplified considerably by using a
PNP transistor as an emitter follower (commoncollector circuit) with DC coupling, as shown in
Figure 8. With a sufficiently damped resonant
circuit, the capacitive voltage divider shown in
Figure 7 can actually be omitted because the
internal capacitances of the transistor perform
the same role. In addition, this circuit can also
operate with a low supply voltage, such as 1.5 V.
If you like to experiment with DIY mediumwave radios, you may wish to have a modulated
oscillator for test purposes. A test transmitter
of this sort is not connected to an antenna and
therefore does not disturb your neighbours.
Instead, the RF energy is transferred directly
from one coil to the other.
However, the oscillator needs to be stable, as
otherwise there’s little point to such a modulated
signal generator for medium-wave frequencies,
but crystals for these relatively low frequencies
are very expensive. For this reason, ceramic
resonators are often used in such cases.
Resonators with rated frequencies of 500 kHz
or 2 MHz are commonly available, but these
frequencies are outside the medium wave band.
However, resonators are also available with
frequencies that fit better. For example, we found
a ceramic resonator with a frequency of 986 kHz
in a discarded television remote control.
Figure 10 shows the circuit of a complete AM
test oscillator. The trimmer can be used for fine
tuning. If a broadcast station (most likely weak)
can still be heard in the background, you can
simply tune the oscillator to a beat frequency
that neutralizes the station, such as 981 kHz. The
small ferrite coil in the transmitter couples directly
to the ferrite rod in the receiver. Incidentally, with
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relatively minor alterations you can also use this
circuit in the short wave region, for example at a
frequency of 13.56 MHz, which can be used for
experimental purposes without a license.
The modulator stage is designed as an emitter
follower that modulates the supply voltage of the
output amplifier stage. As monaural transmission
is still standard in the medium- and short-wave
bands, the signals from the left and right stereo
channels are combined at the audio input. The
potentiometer should be adjusted for the lowest
distortion and the best sound quality. The RF
amplifier stage has been intentionally kept
modest, since high power is not the objective
here.
+9V
modulator
100k
27k
BC547B
1k
10k
10n
470n
680uH
330p
output stage
470k
30p
976kHz
BC547B
10k
oscillator
GND
60p
27k
27k
BC547B
Short wave regenerative receiver
with feedback
The three-stage short wave receiver shown
in Figure 11 has an additional control for
the feedback. The first stage is essentially an
oscillator corresponding to the circuit in Figure 8.
However, its operating point can be adjusted as
desired to vary the gain. Here the trick is to
adjust the gain to just balance out the losses of
the resonant circuit, so that the circuit is just on
the edge of oscillation. At this point the receiver
has the highest gain and the best selectivity.
The PNP oscillator stage in the common-collector
configuration is also the regenerative stage that
demodulates the HF signal. The two following
audio stages generate enough power to allow a
small loudspeaker to be used.
ANT.
L
R
This brings us to the end of the Electronics for
Starters series. However, we intend to continue
presenting articles on basic aspects of electronics
at irregular intervals in upcoming issues of the
magazine. Some of the topics on the agenda are
operational amplifiers and commonly used digital
ICs. Stay tuned for more!
Figure 10.
A modulated medium-wave
AM signal generator.
(120010)
Internet Links
Figure 11.
A regenerative receiver with
feedback.
1k
2k2
4k7
47u
10k
32
BC557C
3k3
1V5
12p
470u
10u
100n
330p
150p
1n
BC547B
470k
470k
Whether the regenerative stage can be adjusted
to the edge of oscillation depends in part on
how much the input circuit is damped by the
connected antenna. For this reason there are two
options for connecting the antenna. Connection
through a small coupling capacitor results in loose
coupling and low damping. By contrast, direct
connection is suitable for very short antennas,
since a relatively long antenna also radiates HF
energy, thereby damping the resonant circuit.
With the right setting, extremely high sensitivity
can be achieved with a regenerative receiver.
Such receivers were standard equipment in the
early days of radio engineering. Even with weak
transmitters, they achieved ranges of several
thousand miles. You can still experience the
fascination of this circuit today, since it allows
outstanding receivers to be built with very low
cost and effort.
1n
BC547B
4n7
15 turns
74874
Projects
Transconductance
Amplifier
Voltage in,
current out
A transconductance amplifier is a special differential amplifier where the output
current is a function of the difference in the input voltages. With the help of an
AD844, made by Analog Devices, it becomes a simple matter to create such a
circuit. A transconductance amplifier like this can be used as a versatile amplifier
stage for a wide range of measurement functions, as you’ll see in this article.
By Wim de Jager
(The Netherlands)
The AD844 opamp is primarily designed for use
in current feedback applications, but due to its
particular structure it can also be used in an
open loop configuration as a dependent source.
Because of this, it’s fairly easy to use this opamp
as a voltage controlled current source (transconductor), which can be used in various aspects of
measurement functions. This article describes
the inner workings of the AD844, the design and
construction of a pre-amp using this IC and several examples of its use.
AD844
R1
R3
C3
10M
3M
C1
2p
4p5
B1
B2
I in
C2
R4
15R
Vo
I in
2p R2
Operation of the AD844
A functional diagram of the AD844 is shown in
Figure 1. Buffer B1 is used to obtain a + input
with a high impedance and a – input with a low
impedance. The generated current Iin in the internal circuit is also available at the external pin
TZ, the output of the V/I converter (also called a
transconductor). Iin in the pre-amp is meant for
driving external components or networks. The
voltage at TZ is made available at the output
via B2. Resistors R1 to R4 and capacitors C1 to
C3 are there to compensate for the non-ideal
behaviour of the opamp. The values given in
the diagram come from the documentation of
Analog Devices [1].
When a voltage differential Vin is connected
between the + and − inputs, the transfer function is Iin/Vin = 1/R2 = 20 mA/V. When no load
is connected to TZ, Ao = R3/R2 = 60,000. The
bandwidth depends on R3||C3, which is f3dB ≈
12 kHz with the values in the circuit.
TZ
50R
The design of the pre-amp
Figure 1.
Functional diagram of the
AD844.
120433 - 11
The design for the pre-amp (see Figure 2) includes
a circuit that provides bias current compensa-
74874
Transconductance Amplifier
R6
R9
1k5
22k
R8
D1
100R
C2
The input resistance is mainly determined by
R1. The bias current of the + input of the opamp
creates a voltage across R1 of 10 mV when the
POS.IN connection is open circuit. Since the offset of the opamp is very small, it can be useful to
compensate for the effect of the bias current in
certain applications (AC coupling or high source
impedances). Since the direction of the bias current can vary due to the effect of tolerances in
complementary circuits, the adjustment range of
the circuit around P1 was designed to be −23 mV
to +23 mV. Resistors R7 and R8 ensure a low
resistance path for the wiper of P1 to ground.
When POS.IN is driven by a source with a low
output impedance there is no need for the compensating circuit. This circuit is not suitable to
compensate for the internal offset of the AD844.
R1
D2
C1
100k
100R
220n
3V9
P1
1N4148
470n
R2
POS. IN
2
1k
R3
3
1k
NEG. IN
IC1
7
AD844
5
R4
R i = 68
Vo
R o = 16
6
4
ZTZ =
6M // 10p
18k
TZ
D3
D6
D8
1N4148
D4
220n
3V9
D9
3V9
D5
D7
R12
1k5
4R7
R10
22k
R5
D10
C3
100R
R7
D5...D8 = 4x
–15V
from Figure 1. On TZ you can connect any type
of component (also semi-conductors) or a network. Since there is no feedback there aren’t any
stability issues. The impedance ZTZ does introduce a measurement error, but the value of this
is very small in most applications. The voltage at
TZ (Vo) is made available via buffer B2.
With the help of the diode circuit consisting of D5
to D10 an overload detector has been added. Vo is
BAT43
120433 - 12
Figure 2.
Complete circuit diagram of
the amplifier,
using an AD844.
IC1
78L15
D2
TR1
+15V
1N4005
C2
230VAC
(115VAC)
12V...15VAC
The maximum permissible voltage between the
input terminals is 5 VDC and the clipping circuit
consisting of D1 to D4, R9 and R10 protects
the input against an overload. We have chosen
1N4148 Silicon diodes for D2 and D3. Schottky
diodes haven’t been used in this case because
they have a relatively large reverse-bias current,
which would cause an unwanted DC offset. When
a ¼ W type is used for R2, the maximum input
voltage may be 20 VDC. It is also possible to use
a metal film 1 kΩ, 2 W resistor, in which case
50 VDC is permissible. Large values for R2 (as
well as wirewound types) have a negative impact
on the HF response. When a coupling capacitor
is used, the clipping circuit plays an important
part to prevent any damage from occurring to the
AD844 from the current spike that occurs when
the capacitor is charged up. For the transconductance a value was chosen of 1 mA/V, from
which follows that R3 = 1 kΩ. Resistor R4 compensates for the effect of Ri. With a value of 1 kΩ
the current at 5 VDC is equal to 5 mA, which is the
maximum value according to the specifications
for the AD844. With these settings the AD844
functions optimally.
+15V
R11
4R7
tion, a clipping circuit to protect the positive input
(POS.IN) and an overload detector for the output
voltage (Vo). For all applications in this article the
negative input (NEG.IN) is connected to ground.
The input signal at POS.IN is connected via R2
to the + input of the AD844.
470u
35V
C1
D1
1N4005
TZ is the output of the voltage controlled current
source as well as the input of internal buffer B2
470u
35V
79L15
IC2
–15V
120433 - 13
Figure 3.
The associated power supply
uses an AC power adaptor.
Through the use of halfwave rectification we obtain
symmetric supply voltages
from a single secondary
winding.
74874
Projects
tection against overloads (max. 100 mA) and
short circuits.
Implementation
Figure 4.
The insides of the prototype
built by the author.
full-wave rectified via diodes D5 to D8 (Schottky
diodes are used for these because of their low
forward voltage drop and their good HF properties) and this signal is fed to the series circuit
of zener diode D9 and LED D10. When the LED
just lights up the distortion is about 0.5 % due
to the maximum output limits being exceeded;
a bright light indicates that severe clipping is
taking place. The filters R11/C2 and R12/C3 are
important for the stability of the AD844. Analog
Devices recommends that they are included in
any design.
The power supply
A mains adapter has been used for the power
supply (see Figure 3). The secondary voltage is
12 VAC at 500 mA. When it is only lightly loaded,
as is the case here, the secondary voltage of the
transformer rises to about 15 VAC, which is sufficient for this application. In order to obtain a
symmetrical power supply of ±15 V from a single
secondary winding it is necessary to use halfwave rectification. With the use of large electrolytic smoothing capacitors this won’t be a problem
though. Voltage regulators IC1 and IC2 provide
a stable output voltage and also provide pro-
0.60Vrms/div
Figure 5.
An impedance measurement
of an inductor, made with
a USB scope with a built-in
function generator. 0.6 V/div
corresponds to 6 kΩ/div, with
the maximum of 6 V being
the equivalent of 60 kΩ.
Top: 6.00Vrms/div
Phase: +/- 180deg 36deg/div
For the enclosure, see Figure 4, use is made of
an enclosed aluminium box with a tinned copper-plated board inside. The tinned layer of this
board is used as a ground plane for soldering
the ground connections to. BNC connectors have
been chosen for the inputs and the output, with
banana plugs used for the TZ connections. The
DIL socket for the AD844 is mounted on a small
breakout board, which you could make yourself if
necessary. Diodes D5 to D8 have been soldered
onto PCB pins that have been inserted into the
DIL socket. P1 is a 15-turn cermet potentiometer, which can be used to precisely set the bias
compensation. The complementary bipolar transistors inside the AD844 have a high fT, which
makes a careful layout essential in order to prevent parasitic oscillations. The ground plane in
conjunction with short connections are the best
guarantee for good HF specifications and stability.
Measurements on the pre-amp
The effect of the internal offset of the AD844
was measured with a micro-ammeter, which
was connected to TZ, when the input terminals
were shorted together. The measured value was
0.1 µA, which is so low because of the use of
laser trimming to minimise the offset. If required,
the offset can be reduced even further using an
offset circuit described in the documentation for
the AD844. With the POS.IN input open circuit
the bias current of the + input creates a voltage across R1 of 10 mV, which results in a current of 10 µA at TZ. This value is much larger
than the offset so it makes sense to include the
bias compensation circuit just described. With
this circuit it is possible to reduce the current to
under 0.1 µA.
The AC response when no load is connected to
TZ was measured with an input signal of 0.5 mV
at 500 Hz. The gain was then found to be 6000.
Since 1 mA/V × RTZ = 6000, it follows that
RTZ = 6 MΩ. The −3 dB frequency is at 2.5 kHz.
ω × RTZ × CTZ = 1, so CTZ = 10 pF. The measured
value for Ri is 68 Ω. For Ro the value is 16 Ω.
Measurements on capacitors and
inductors
10kHz
120433 - 14
1MHz
Connect a capacitor to TZ and a sinewave generator to POS.IN. Then set the amplitude to say
Advertisement
74874
about 500 mV and adjust the frequency (preferably from
high to low so as to avoid any overloads) to a value where
the voltage at TZ is also 500 mV. At this frequency the value
of the gain is 1 and it’s possible to calculate C from the formula R = 1/ωC, from which follows that C = 1/ωR.
As an example, for a connected capacitor a gain of 1 occurred
at a frequency of 16 kHz. Since R = R3 = 1 kΩ, the formula
gave a result for C of 10 nF. When a Voltcraft 9036 LCR
meter was used to measure this capacitor it was found to
have a value of 10.47 nF.
DEEP MEMORY
MIXED SIGNAL
OSCILLOSCOPES
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For the measurement of self-inductance we also recommend a generator voltage of about 500 mV. In this case
the frequency should be adjusted from low to high in order
to avoid any overloads. When an inductor with a toroidal
core was connected we found that a gain of 1 occurred at
56 kHz. In this case ωL = R and L = R/ω = 2.84 mH. When
the LCR meter was used we obtained a value of 2.86 mH.
It is also possible to calculate the self-capacitance of an
inductor winding (Cp) from the frequency at which self-resonance occurs. For this particular inductor this frequency
was found to be 360 kHz. Since Cp = 1/ω02L, the calculated
value was 69 pF. However, to obtain the correct value you
have to deduct CTZ = 10 pF, which means that the true value
for Cp is 59 pF. At self-resonance the impedance is equal to
the parallel equivalent resistance, which can be determined
from the measured gain. The value of the gain was 38, from
which follows that Rp = 38 × R3 = 38 × 1 kΩ = 38 kΩ.
Impedance measurements with the Velleman
PCSGU250
The PCSGU250 USB oscilloscope from Velleman contains a
built-in function generator. It is possible to use it as a circuit analyser with the help of the associated software. With
this combination it is possible to create Bode plots, where
the modulus and argument of the transfer function of an
electronic circuit is shown as a function of frequency. The
V/I converter of this pre-amp makes it possible to measure
the modulus and argument of an impedance. This type of
meter is sometimes called a vector impedance meter because
the phase is measured as well. In Figure 5 you can see the
impedance and phase characteristics of the inductor used
previously. The phase is about 90° up to about 200 kHz,
which is to be expected for an inductor. At 370 kHz the selfresonance can be seen, from which the parallel equivalent
resistance can be determined. Since the amplitude of the
generator is 100 mV is, the vertical scale for the modulus (Y)
is 6 kΩ/div. The measured value for Rp is 34 kΩ in this case.
Measurements on semiconductors
A current output is also useful for measuring the characteristics
of semi-conductors, such as bipolar transistors. A measure-
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www.USBmso.com/PS170
74874
Projects
–5V
D1
BAT43
T1
TZ
BD139
Figure 6.
The circuit for carrying out
measurements on an NPN
transistor.
VS
1R
R1
120433 - 15
ment circuit for an NPN transistor is shown in Figure 6. The −5 V power supply at the emitter makes
it possible to connect the measurement resistor
(R1) to ground. The voltage across this resistor (1 Ω) is proportional to the collector current.
The TZ connection of the pre-amp is connected
to the base of the transistor. The base current is
equal to 1 mA/V. Schottky diode D1 protects T1
against high reverse-biased voltages. The β graph
was measured with an oscilloscope (see Figure 7),
the vertical being the voltage across R1 and the
horizontal the voltage at POS.IN. The vertical sensitivity is set to 0.2 V/div, which corresponds to
0.2 A/div for the collector current. The horizontal
sensitivity is 1 V/div and that corresponds to 1 mA/
div base current. Since the signal at Vs is negative the ‘invert’ mode (which may not be found
on every oscilloscope) was selected to obtain a
positive display. From the graph you can work
out that at Ic = 400 mA the current gain β = 118.
The second example is for the measurement on
a zener diode, see Figure 8. The horizontal scale
is 0.5 V/div, which corresponds to 0.5 mA/div for
the current through the zener diode. The vertical
scale is 1 V/div, which is for the voltage across
the zener diode. At a current of 2 mA the zener
voltage is equal to 3.6 V, which was exactly what
was expected from the specifications.
Pre-amplifier
A DC-coupled preamplifier can be created very
easily by connecting a load resistor (RL) to ZT.
For example, with RL = 10 kΩ the gain is RL/
R3 = 10. The bandwidth can be calculated from
RL||CTZ and is equal to 1.6 MHz. Measurements
have confirmed these values. A possible use for
the pre-amplifier is to improve the sensitivity of
any measurement equipment.
Buffer
The output buffer can also be used as an independent voltage follower, with TZ as the input
and POS.IN grounded. The bandwidth is about
10 MHz. The input impedance is equal to
ZTZ = 6 MΩ//10 pF and the output resistance
is Ro = 16 Ω. The maximum output voltage is
5 Vrms with a THD of 0.7% (1 kHz). The maximum output current is 80 mADC and the circuit
is protected against short circuits.
Figure 7.
This is the scope display
when a measurement is
carried out on the circuit
from Figure 6. Horizontal
1 mA/div, vertical 0.2 A/div.
(120433)
Internet Link
[1] www.analog.com
Figure 8.
The display of a
measurement on a zener
diode. Horizontal 0.5 mA/
div, vertical 1 V/div.
74874
DESIGN
DESIGNSPARK
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DESIGNSPARK PCB
VERSION 4
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UNIQUE
RESOURCES BY
30-10-12 15:53
74874
Projects
PWM to phase shifter
By
Stephen Bernhoeft
In some situations it can be useful to vary the
phase between two square waves. In the schematic shown in Figure 1, the two D-flipflops ‘A’
and ‘B’ convert the PWM signal into a square
wave in the standard manner. However, D-flipflop
‘A’ is clocked by the rising edge of a pulsewidth
modulated (PWM) signal, whereas D-flip flop ‘B’
is clocked by the falling edge. This way the duty
cycle of the PWM signal determines the phase difference between the outputs of the two flipflops,
as illustrated in timing diagram Figure 2. A limitation is that phases 0 and 2 pi are not possible.
A possible variation would be to replace both A
(United Kingdom)
and B by quadrature output blocks. If then Q0 is
taken from the ‘I’ (in-phase) output of block A,
and Q2 is taken from the ‘Q’ (quadrature) output
of block B, a phase difference of pi in the original scheme maps to a phase change of 2 pi. Of
course, then ‘exactly pi’ (i.e. quadrature) phase
difference would be impossible.
If the PWM is microprocessor controlled, then the
relative phases can be made to cross because
(for example) a ‘trailing Low’ may be ‘stretched
into a ‘leading Low’, as pictured in Figure 3.
(120193)
CLR
T1
D
R
A
D-flipflop
CLK
S
Q0
Q
T1
T2
PWM
Q
Q0
T1
PWM
D
R
B
D-flipflop
CLK
S
T2
Q1
Q
T2
Q1
Q
1
2
3
Improving the pick-up angle of an
infra-red satellite receiver remote
By Géry Szczepanski
+5V
100R
4u7
100080 - 11
When the TV is on a rotating base and the satellite
receiver remains fixed, the infrared remote sometimes has trouble getting through to the satellite
receiver. This is easy to put right if you’re a bit
of a DIYer, as all you have to do is add a second
infra-red detector in parallel with the receiver’s
existing one. This can also be applied to a DTT
decoder, TV, etc. Here’s how to go about it for
an XSAT CD TV360 satellite receiver.
Open the satellite receiver, unclip the front panel
and hinge it downwards with its PCB. Identify
the ground, +5 V rail and the ‘signal’ terminal
(using a voltmeter, it is at +4.5 V). Fit the circuit
74874
Design Tips
show here in parallel with the existing detector. Close the satellite receiver back up again.
The second IR detector is attached to the TV using
a spot of glue. Under these circumstances, the
satellite receiver could even be located inside a
unit, a drawer, behind a piece of furniture, etc.
(but don’t forget to think about ventilation).
Watch out, plugging the jack in or out must not
short out the 5 V rail, even very briefly.
(100080)
Audio amplifier in dinner mint format
be appreciated in view of the high sensitivity of
the TDA7052. If required, this can of course be
a real potentiometer with knob and all to adjust
things on the fly.
TDA7052
+6V
0
C1
C2
220u
25V
100n
1
+6V
IC1
TDA7052
Vp
5
P1
2
10k
3
LS1
6
8
There are countless situations and systems devisable in which a sound signal needs to be amplified in order to drive a (small) loudspeaker, but
where space constraints rule out the use of a
regular sized amplifier. For these situations, this
sub miniature amplifier is perfect. With some
skills it can be assembled to a size smaller than
an after dinner mint!
The TDA7052, which was released by Philips a
many moons ago, is a typical example of a fully
integrated circuit. The only external components
required are two decoupling capacitors. That’s all.
In the circuit diagram of the amplifier you can
find an internal schematic of the integrated circuit. It’s easy to see two amplifiers connected
in a bridge arrangement. This is done in order
to squeeze a ‘decent’ power from the IC at relatively low supply voltages.
A preset has been added to the input to prevent the circuit from being overdriven, this will
By
Ton Giesberts
(Elektor Labs)
Maximum power output is just over 1 watt, which
is more than enough for most applications. The
power supply voltage can be up to 18 V, but be
aware that voltages above 6 V or so can cause
the IC to become hot. When using higher voltages, use a loudspeaker with an impedance
greater than 8 ohms or limit the input signal of
the amplifier. Don’t worry about FUBR-ing the
amplifier though. Even though the IC heats up,
an internal thermal security will stop anything
from blowing up.
A few measurements were carried out on the
prototype and the results in the table below show
what happened at a supply voltage of 6 volts and
a loudspeaker impedance of 8 ohms:
THD+N*
Pmax
0.09% (1 kHz, 100 mW in 8 Ω), 0.3% (20 kHz, 100 mW in 8 Ω)
750 mW (THD+N = 1%)
1 W (THD+N = 10%, heavily clipped output signal**)
Gain
38 dB (P1 at maximum)
Supply voltage
3–18 V
Current
consumption
5 mA (quiescent), 340 mA (1 W continuous power output)
* THD+N = Total Harmonic Distortion plus Noise
** clipping only noticeable at 2% distortion.
Pretty good results for an amplifier this simple!
The construction of this mini amp is unlikely to
cause problems. If you work neatly, the circuit
will most definitely work. Some people have
taken it as a challenge to make the circuit as
small as possible.
Whatever you choose to do, we wish you a lot
of fun tinkering!
(i-00909)
74874
Industry
Creating a
Low-Leakage Rectifier
using a self-powered opamp
By Martin Tomasz, Senior Scientist, Touchstone Semiconductor, Inc.
VGATE = VOUT – (R2 / R1) × (VIN – VOUT)
T1
R1
100k
BSH205
R2
VGATE
1M2
VSS
VDD
IC1
TS1001
C1
10u
120517 - 11
Figure 1.
This circuit emulates a
rectifier, but it has forwardvoltage drop of 40 mV or
less. The circuit has less
reverse leakage than a
Schottky diode.
A nanopower opamp, a low-threshold P-channel
MOSFET, and two feedback resistors are combined
to make a rectifier circuit with less forward drop
than a diode (Figure 1). Since the rectified output voltage powers the active circuitry, no additional power supply is necessary, and the circuit’s
quiescent current is lower than most Schottky
diodes’ reverse-leakage current.
This circuit provides active rectification at voltage drops as low as 0.8 V. At lower voltages,
the MOSFET’s body diode takes over as an ordinary diode.
When a forward voltage develops between the
input and output voltages, the opamp circuit
turns on the MOSFET, according to the following equation:
About the author
Martin Tomasz is a seasoned analogue, radio, and mixed-signal
engineer with 22 years’ experience in circuit and systems design. As
senior scientist at Touchstone Semiconductor, Martin has 17 patents
to his credit. Prior to joining Touchstone Semiconductor, Martin spent
two seasons in Antarctica working for the US Antarctic Program,
working with scientific monitoring devices designed to work in extreme
environments.
where VGATE is the MOSFET’s gate drive, VIN is the input
voltage, and VOUT is the output voltage. The input and
the output voltages to the MOSFET’s drain-to-source
and gate-to-source voltages are described by the following equations:
VDS = VIN – VOUT and VGS = VGATE – VOUT
where VDS is the drain-to-source voltage and VGS
is the gate-to-source voltage. Algebraically, these
equations relate to the MOSFET’s gate drive to a
function of the drain-to-source voltage:
VGS = –(R2 /R1) × VDS
A good design choice is to make R2 12 times
larger in value than R1, resulting in a 40-mV voltage drop across the MOSFET’s drain-to-source
voltage, sufficient to turn on the MOSFET at low
drain currents (Figure 2). A higher ratio further
reduces the voltage drop within the limits of the
opamp’s worst-case input-offset voltage of 6 mV.
Power for the opamp (the Touchstone Semiconductor TS1001) comes from the circuit’s output-the output-reservoir capacitor C1. Since he
amplifier has rail-to-rail inputs and outputs and
no phase inversion when operating near the rails,
connecting its supply rails to the output works
well. Additionally, since the amplifier operates at
power-supply voltages as low as 0.8 V, the circuit’s rectifying action works to this low voltage.
The opamp’s non-inverting input is connected to
the VDD rail and the amp’s output to the gate of
the MOSFET. The circuit consumes slightly more
than 1 μA when actively rectifying a 100-Hz sine
wave, less current leakage than that of most
Schottky diodes. The BSH205’s threshold is low
enough to support milliamp-level currents at a
gate-to-source voltage of 0.8 V.
74874
Low-Leakage Rectifier
A micropower solar-harvesting application is
shown in Figure 3. The BPW34 cells generate
10 to 30 μA at 0.8 to 1.5 V, depending on the
light. This circuit rectifies the peak harvested
voltage in conditions of rapidly changing light
and minimizes reverse leakage to the cells at
low light conditions.
Figure 2.
The output of the circuit
(green) with a sinewave
input (yellow) shows that
the FET’s gate voltage (blue)
drops out only when the
input-to-output differential
is less than 40 mV.
SOLAR HARVESTED
T1
R1
D1
R2
D2
POWER
BSH205
100k
The opamp’s bandwidth does limit the circuit to lower-frequency signals; at bandwidths
higher than 500 Hz, the amplifier’s gain begins
to decline. However, as the signal frequency
increases, the body diode of the MOSFET takes
over the rectification function while the MOSFET
remains off. Fast fall time input signals could
potentially drag the output with reverse current
through the MOSFET, before the opamp has a
chance to turn the MOSFET off. However, for
small currents, the MOSFET operates in its subthreshold range. On the other hand, the amplifier
quickly turns off due to the exponential relationship of the gate-to-source voltage to the drainto-source current in the sub-threshold range.
Ultimately, the amplifier’s slew rate of 1.5 V/ms
is the limiting factor. As long as the circuit’s load
is light enough to keep the MOSFET from operating in its linear range, reverse currents won’t
exceed forward currents.
VGATE
2M2
VSS
D3
3x
BPW34
(120517)
VDD
IC1
TS1001
C1
400u
ceramic
120517 - 13
Figure 3.
You can use the activerectifier circuit to charge a
capacitor from solar cells.
The rectifier has a low
voltage drop and protects
the cells from reverse
current when there is no
light.
World’s smallest
humidity and temperature sensor
Sensirion’s tiny SHTC1 humidity and temperature sensor is specifically designed for
mobile devices where size is a critical factor. Sensirion has rigorously followed the
maxim “smaller is better” and developed the world’s smallest sensor in its class,
measuring a mere 2 x 2 x 0.8 mm. The sensor is based on the proven CMOSens®
Technology, which allows the sensor and the signal processing electronics to be
combined on a single silicon chip to achieve small device size. Production is targeted at high volume to allow low unit prices to be achieved by economy of scale.
The supply voltage of 1.8 V is also fully in line with the needs of the target industry.
The specifications of the new sensor show that the size, power consumption and price reductions do not have any impact on performance.
It measures relative humidity over a range of 0 to 100 %RH with a typical accuracy of ±3 %RH. The temperature measuring range is -30 to
+100 °C with a typical accuracy of ±0.3 °C. The sensor is fully calibrated, has a digital I²C interface, and is suitable for reflow soldering. This
makes it compatible with standard industrial mass production processes for electronic modules. To ensure effective integration of the sensor
in complex applications, Sensirion draws on its many years of experience with sensor products deployed in the millions and supports customers with corresponding application expertise. The new SHTC1 humidity and temperature sensor combines extreme miniaturization with top
performance, and with Sensirion’s implementation support it is doubtless a decisive step ahead of the competition.
www.sensirion.com/shtc1
(120663-II)
74874
Industry
State-of-the-art audio to truck cabs and buses
STMicroelectronics has introduced the market’s most powerful and most simple-to-use
audio power amplifier for commercial vehicles such as trucks,
buses and agricultural vehicles,
whose electrical systems run at
24 V rather than the 12 V used
in cars. It is the world’s first
audio amplifier that can drive
the cabin loudspeakers directly,
without any external components, in 24-V vehicles, confirming ST’s dedication to the heavy-vehicle segment.
Audio amplifiers used in automotive systems must be
designed to withstand the demanding automotive environment, including a high level of electrical noise and
the need to provide comprehensive protection against
potential hazards such as short circuits, load dumps, and
excessive chip temperature. Audio amplifiers for use in
12-V automotive systems have reached a very high level
of sophistication, but up till now audio equipment manufacturers have been unable to replicate this performance
in 24-V systems without using external components that
not only drive up the Bill of Materials cost, but can even
compromise safety under certain conditions.
ST’s TDA7576B 24-V audio amplifier uniquely solves
this problem. It is built in a proven high-volume semiconductor manufacturing technology called BCD5 that
allows a single chip to include both the power blocks
and the signal management blocks — so there is no
need to use a more expensive multi-chip approach
— and it can sustain a peak supply voltage of 60 V
without any damage. The most powerful audio power
amplifier for 24-V systems available on the market, the
TDA7576B has been designed with the same guidelines
and care that ST uses for car radio audio power amplifiers, so the final user can enjoy the same high-quality
audio as car drivers.
The TDA7576B audio amplifier expands ST’s dedicated
portfolio of products for 24 V vehicles that includes
recently announced chips for exterior and interior lighting.
Key features of the TDA7576B include:
•24V battery operation;
•High output power (2 x 20 W);
•Minimized external components (no decoupling
capacitors, no bootstrap capacitor and no external
compensation components);
•Integrated power-saving standby function;
•Diagnostic output pin that alerts the host controller
in the event of clipping, short circuits or excessive
temperature;
•Output DC offset detection;
• Protection against 60V load dump, excessive chip
temperature, ESD (Electrostatic Discharge) and output short circuit to GND, Vcc, or across the load.
The TDA7576B is available now in a compact Multiwatt15 package.
www.st.com/internet/automotive/product/254152.jsp
(120605-V)
Magic PCB and more from Beta LAYOUT
Beta LAYOUT’s newest innovation ‘Magic PCB’ was be unveiled at this year’s electronica
exhibition in Munich, Germany. Beta LAYOUT has developed a groundbreaking application machine to embed RFID chips into a printed circuit board. The chips are embedded
during the initial production steps allowing for identification and traceability from the
onset. RFID chips have a high reading accuracy with the added advantage of an invisible copy protection. The RFID chips function within the UHF frequency bands (860 MHz to 960 MHz) and can be operated globally.
The second highlight at the Beta LAYOUT booth was their new online IDF-to-3D tool (IDF=Intermediate Data Format). Using any printed circuit
board software that outputs IDF data this tool allows design engineers to create a 3D data model of their assembled printed circuit board. This
powerful 3D conversion tool enables the design engineer to check and verify the dimensions and position of components, such as keyboard
sections, plugs, sockets etc. on the soft version before freezing the design. Beta LAYOUT continues its unique relationship with EAGLE users
by developing a specific ULP (User Language Program) to interface with the IDF-to-3D tool specifically for them. Beta LAYOUT offers this free
of charge to its loyal EAGLE user customer base.
www.betalayout.com
(120663-III)
74874
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Naamloos-4 11
Naamloos-8
20-08-12 11:17
11:50
09-11-12
74874
tech the future
The Internet of Things
By Tessel Renzenbrink (Elektor TTF Editor)
the Internet of things (Iot) is
the merger of the physical and
the digital world. Ordinary objects featuring tiny computers
will be assigned an IPv6 address
and have a digital representation on the Internet. We will be
able to access information about
the objects in our daily lives over
the internet and even remotely
control them.
Many instances of the Iot won’t even have
humans in the loop. the Iot as a machine-tomachine network where sensors and actuators
communicate with each other to move the environment to a desired state.
In September the workshop rOBIOtS: robots
Meet Internet of things took place as part of
the two-day PIcNIc festival for media and innovation, hosted in Amsterdam. Afterwards I discussed the future of Iot, its technological challenges and its potential dark side with three of
the speakers: florian Michahelles, heico Sandee
and Stefan Gessler.
The IoT experts
Dr. florian Michahelles is the associate director
of the Auto-ID Labs Zurich/St. Gallen. the AutoID Labs are the leading global network of seven
academic research laboratories in the field of
networked rfID. his research interests centre
around the Internet of things.
Dr. heico Sandee, program manager at the Department of Mechanical engineering at eindhoven
technical university, is specialized in control systems. he participates in the roboearth project, a
multi-disciplinary partnership of robotics researchers from academia and industry aiming to create
a world wide web for robots.
Stefan Gessler is project manager at the Software
and Service research Division of Nec Laborato-
ries europe. he participates in the florence project, an activity to make low-cost robots interact with a smart home environment to support
elderly people in their daily life at home. he is
also involved in the formation of the Iot-forum.
The purpose of the IoT
Tessel: Why does the world need the IoT?
florian: One answer is: it just happens. It’s just
the natural evolution of technology.
heico: It’s about span of control. I am so used to
having the power at my fingertips to communicate with everyone, I find it almost stupid I can’t
communicate with the things in my life. I want
to be able to check on my phone whether I forgot to lock my door. I want to have access to this
information and even be able to close it remotely.
Stefan: the Iot is all about cooperation and communication. communication is a prerequisite for
cooperation. You can think of thousands of scenario’s in which it is an advantage when things
work together. for instance, a sensor detecting
water on the bathroom floor can signal the water
tap to close itself. Or a car detecting a safety hazard ahead telling the cars behind it to slow down.
heico: And it opens up entirely new possibilities.
In the roboearth project we’re creating a system to exchange information between objects,
robots and humans. Say, you connect your coffee machine to your alarm clock. As soon as the
74874
Tessel: What are the technological challenges of
realising the IoT?
Stefan: the biggest challenge is the modelling
of information. to enable every device to communicate and to cooperate with all other devices.
What happens a lot at the moment is the so called
silo-approach. You have a certain application field
and devices designed to execute one particular
task. this system is a closed box consisting of
sensors, actuators and software. If you want to
add a second application you have to buy it all
again, the sensors, the actuators but this time
with different software and protocols. the next
step we have to take is reusing the data, sharing
it among the devices. But that means you need
to have an interoperable interface. that is what
we are working on at the moment.
florian: At the Auto-ID labs we focus on the product side: how to make the flow of items and the
supply chain more efficient. the idea is to have
a barcode or uniquely identifiable rfID number that is associated with data describing the
type of product. And now we recognize that the
barcode –a forty year old technology- can also
be useful for consumers with smartphones. But
the consumer is interested in different data. he
isn’t interested in the size or the weight of the
product but in the ingredients or its application.
And next we have to derive semantics from the
data which can be interpreted by robots. In the
Iot different systems that emerged for different
reasons have to work together.
But standardization isn’t so much a technical
Internet infrastructure
Tessel: The Internet is the backbone
of the IoT. Is the current state of the
Internet infrastructure sufficient?
Stefan: We will need increasingly more
bandwidth. everything is working so far
but we have to be prepared for Big Data.
the growth of data is exponential. As
one of the speakers pointed out in the
workshop: 5 billion gigabytes of data was
created since the beginning of recorded
time. In 2011 that same volume of data
was created in two days. By 2013 we will
create it in 10 minutes. the capacity of
the radio spectrum is inherently limited.
You can’t add an unlimited amount of
devices to the wireless network.
florian: You have to manage the scarcity. today if the Internet is choked
it may take a little longer for you to
Heico Sandee.
Technological challenges
challenge but rather an organisational
and motivational one. Because it isn’t
one company providing all the infrastructure but many disparate parties.
how do you get all the parties to play
together? Indeed, you have the data
generated by one company but what
is the incentive to share? So the question really is: what is the ecosystem?
What is the business case you can set
up that makes the different parties willing to share because they mutually benefit from it?
heico: I agree that interoperability is
the biggest challenge but is it really
such a big problem? Isn’t it a matter
of making a choice and sticking to it?
Stefan: It is about making a choice but
in this choice you have to consider all
the cases which could possibly appear.
florian: exactly, that’s the point. You
have to understand what you need it
for. technologically it is difficult to build
a solution that fits every case. So it is
easier to agree on, say, five cases and
get a standard on it.
Stefan: the Iot is going to develop bottom up. We will not build an Iot system
and switch it on like we once did with
tV technology.
Stefan Gessler.
alarm goes off the machine starts making coffee.
this is already possible if you have a smart coffee
maker. But what if the machine runs out of coffee? this is where the robot comes in. Because it
has the capability to move it can refill the coffee
bean container. robots will give arms and legs
to the Internet.
And when robots are part of a network they can
learn from each other. roboearth is building a
cloud-based database which can be accessed
by different kinds of robots. When a robot has
solved a problem it can add this information to
the cloud so that the next robot encountering
the same problem can download the instructions.
this way you don’t have to plan for every possible problem in the design phase of the robot,
or equip them all with a large array of sensors
to give them learning abilities.
Florian Michahelles.
the internet of things
74874
tech the future
download that picture. Most of the data traffic
isn’t urgent. But with the Iot it might be different. there might be health applications involved
which depend on permanent access. to manage the scarcity you may have to give priority
to health applications or have users pay a little
fee for priority access. I think we will always be
at the limits of bandwidth but I don’t think it is
a showstopper for the Iot.
Stefan: On the contrary, the Iot could contribute
to a more efficient organization of data traffic.
It’s about making decisions as early as possible.
Data relevant to a local network doesn’t need to
be pushed to a remote datacenter. What we see
now is two distinctions: local and the cloud. In
the future we will have different layers, different
levels of cloud. the data will be organized hierarchically: can it stay local, or does it have to be
made available regionally or globally?
Dark side
Tessel: What are the possible dangers of this
technology?
heico: One of the worries is security. We already
see what damage malicious hackers can do to
the Internet. When all kinds of objects are connected to the Internet the impact of systems
being compromised is even bigger.
Stefan: Whenever you introduce something new it
can also be used for something negative. Another
thing is that a new technology always influences
the way we live our lives. Many people consider
changes as a threat, so we also need to take
care about the acceptance of Iot in future. Security, but also privacy are certainly key factors.
florian: A possible danger is transparency. As
humans we are used to understanding why things
happen. With this digital component added to our
world, we may not perceive the cause of occurrences with our senses anymore. that is why we
continuously have to think about designing the
technology in such a way that we always have
a mental model to understand what is going on.
It’s scary if I can’t grasp what’s happening. It
means I’m controlled by something else. that’s
a dark scenario. But in my opinion the worst
case scenario for the Internet of things is if it
doesn’t happen.
Elektor and the IoT
As Stefan Gessler rightly points out, the Iot isn’t
one technology with a single switch-on moment.
rather, it is a boundless sprawl of technologies
and applications many of which are already in
operation. Probably unknowingly, elektor has
already covered many of them. In the November
edition alone I counted five Iot projects, proving that elektor’s new e-departments .LABs and
.MAGAZINe cover Iot without expressly identifying it. We need to work on that!
One of the best known Iot applications is the
smart meter. Serving as the nerve endings of
the smart (electrical) grid, smart meters provide
information about power consumption at the local
level enabling both energy suppliers and consumers to make informed decisions about saving energy. Last month Søren Mikkelsen showed
how to install an S0-compatible electricity meter
that sends detailed power consumption data to
a local or cloud-based database.
In the November edition Benedikt Sauter in his
series “embedded Linux Made easy” described
how to free your elektor Linux board from a lonely
existence by setting up a network connection.
And Jens Nickel introduced the c library for the
elektorBus to make it easier for developers to
add microcontroller nodes. Both the elektor Linux
board and the elektorBus are crying out to be
connected to the Internet.
Also in the November 2012 edition Dr. Joost
Mertens went to the very basics of internet technology when explaining how to build a network
interface card (NIc) using a 8-bit AVr microcontroller. When paired with an old parallel port
camera, the microcontroller allows you to send
video to multiple recipients on a network.
In part 3a of the “Arduino on course” titled ‘connect the physical world to your Android phone’
David cuartielles and Andreas Goransson set out
to teach you how to start building your own Iot.
cheerfully continued this month!
Isn’t it great to discover a trend when you appear
to already have everything at hand that defines
it? Which project in this December 2012 edition
do you think is Iot ready?
(120632)
Internet References
[1] www.autoidlabs.org
[2] www.roboearth.org
[3] http://iot-forum.eu
74874
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For more information of how to become an Elektor Preferred Supplier,
contact Johan Dijk by [email protected]
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07-11-12 10:31
74874
Magazine
The Nagra IV Tape Recorder
A reporter’s delight, ca. 1968
transistors from America, pots from
England, switches from Switzerland,
capacitors from Holland and connectors from Germany. The name
Nagra is derived from the Polish
word for recording. Its quality
and reliability have given the
Nagra legendary status and
one encountered the device
from ice-cold Alaska to
the searing heat of the
Sahara.
The portable tape
recorder era had begun
in the 1950s using models
driven by clockwork mechanisms, with the launch
of the electrically driven
Nagra III taking place at the
beginning of the 1960s. At the
end of that decade came the most widely used
model, the Nagra IV, which is the subject of
this article.
The Nagra draws its power from 12 ‘D’ cell (IEC
R20) batteries, which together account for a third
of the machine’s bulk (Figure 2). The unregulated voltage from these was available for tape
spooling or the playback monitor amplifier. The
latter delivered a crystal-clear 1.5 watts with
remarkable sound intensity and quality. As long
as you were sparing in your use of fast forward/
rewind and loudspeaker playback, a set of batteries would last without difficulty. Later on you
1
By Peter Beil (Germany)
It was once the most celebrated portable tape
recorder in the world – and yet few Elektor readers
will have heard of it. The Nagra (Figure 1) was
a professional device, developed for professional
transportable applications, whether for broadcast
use or picture-synchronized audio recording for
film and television.
Stefan Kudelski, a Pole by birth and its spiritual
father, specified for it the highest standards technically measurable at the time. Its innards contained
2
3
Retronics is a monthly
section covering vintage
electronics including
legendary Elektor designs.
Contributions, suggestions
and requests are welcome;
please telegraph
[email protected]
74874
Retronics XL
4
5
could get rechargeable batteries in this form factor, which meant you were dragging 20 pounds
(10 kilos) around with you.
Internally a reference voltage of –10 volts governed all sections of the circuitry that handled
wanted modulation. If you are wondering about
the –10 volts (we’ll come back to this later), let
it be said that the whole circuitry is based on a
distinctly unusual positive earth potential. This
may be related in part to the germanium transistors used originally. For backward compatibility
this could no longer be altered subsequently but it
caused significant headaches for the burgeoning
accessory industry. A simple contact with another
device could lead to short circuits too, given that
most of these were wired with negative ground.
This would happen when an audio cable with its
screen grounded at each end was plugged in...
Electromechanically there are no major surprises.
The fully encapsulated capstan motor had three
electronically regulated speeds offering 3.75, 7.5
and 15 inch/s (9.5, 19 and 38 cm/s). A sophisticated drive and friction mechanism operated the
feed-out and take-up reels using, as already mentioned, a single motor (Figure 3). At full voltage
this could rewind fairly rapidly, also spool forward
6
at double speed. Special oils and greases, which
could be applied on request by service dealers,
made operation feasible at environmental temperatures between –20 and +50 degrees C (!)
(–4 to +122 degrees F).
The device illustrated, the Nagra 4.2 from the
1970s, optically identical with the first machines,
represents the pinnacle of technical development
for the series. On the front panel we have, besides
the self-explanatory control elements on the
right-hand side two so-called rotary indicators,
normally known as star indicators (Figure 4).
These provided a confidence check of the operating parameters and consumed only a fraction
of an indicator lamp’s current.
The entire electronics were constructed using
discrete components. Good audio ICs were still
under development then and had a poor reputation for reliability, distortion and noise. Only
years later was a model built using ICs. The inputs
and outputs used balanced transformers, whilst
the internal amplifier stages were asymmetric. A
special feature was the floating balanced output
of 4.4 volts amplitude, an order of magnitude
required by the postal telecomms authorities in
those days for transmission lines (Figure 5).
7
74874
Magazine
8
9
10
The device was constructed in
modular fashion, which was pioneering for the time, with a motherboard on which all modules were
arranged. Everything plugged
in, using locking gold contacts
(Figure 6).
Incidentally, if the white automobile fuse at the upper centre upsets
the trained eye of the electronic
engineer, this is actually not original. It’s there because Mr. Kudelski for all his genius did forget one
thing: the fuse...
The team paid particular attention
to the indicating instrument. Here
they had to take into consideration the varying norms or conventions for indication. The ‘Modulometer’ fulfilled these requirements
perfectly, in which the criteria for
accelerating the pointer needle and
handling the inertia of the indication were combined brilliantly
(Figure 7).
Metrologically all three recording
speeds were adjustable individually
for frequency response, equalized
separately for standard and lownoise distortion correction. Even
the HF symmetry and the distortion factors H3 and H4 could be optimised.
Depending on the device we have achieved frequency ranges from 20 Hz in part up to 18 kHz
–2 dB. At an unweighted signal-to-noise ratio
of –60 dB, this could rival any studio machine.
The recorder provided two microphone inputs and
additional user-modifiable inputs (Figure 8). The
mike inputs were implemented either with input
transformers or as electronically balanced current amplifiers. On the earliest models you had
to plug in the preamplifier specific to the type
of microphone (dynamic high and low impedance, condenser mike, etc.) (Figure 9). Later
the preamp was made switchable.
The inputs were adjustable to an extremely high
degree, meaning that the switchable internal preattenuation scarcely needed to be used. In conjunction with a plug-in limiter and a peak level
limiter having a ‘knee’ function, it was hardly
possible to overload the recording. You also had
so-called magnetic ‘tape saturation’, which was
able to ‘stomach’ the additional peaks.
A problem arose with the rather antiquated but
universally used phantom power feed voltage
of 48 volts. At that time it was still technically
impossible to generate this 48 V operating voltage from the approximately 18 volts available.
Naturally Nagra was aware of DC-DC converters
but the square or triangular waveforms employed
spread too far into the wanted signal. (In any
case the converter was located, for reasons of
modularity, at the most sensitive point in the
chain: the microphone input.)
Here the firm Sennheiser assisted, bringing to
market the then revolutionary HF condenser
microphones for low voltage operation. Seen
against 12-volt phantom supplies, the 10 volt
‘T-Power’ feed along the audio conductors (T
stands for Tonaderspeisung [1]; Poland is right
next to Germany) appeared like the Light of the
World (presumably the reason for the internal
10 V reference voltage). For reasons that cannot be fathomed the 12 V phantom version sank
without a whimper, whereas T-Power has held
out a long time. Unfortunately this is not without
some vagaries.
In this system, as its German name implies, the
operating voltage is fed symmetrically along the
two audio conductors, which indeed causes no
interference to the wanted signal. That said, voltage-regulated amplifiers do not enjoy having a
DC voltage on their input at all.
The special current inputs on the Nagra were
fairly indifferent to this but the voltage inputs
needed to have this DC voltage blocked with
two capacitors. Voila: with the combination of
the input resistance and the capacitor you have
created a filter! Unfortunately, in terms of frequency range, this is definitely only a compromise solution.
If you accidentally connect a dynamic microphone
to a T-Power input, all the bass notes disappear,
because the DC voltage magnetizes the moving
coil... But somehow we have tolerated these little problems.
Back to the recording apparatus once more. On
the top side we see another audio head between
the record and playback heads. This was the most
vital element for all sync purposes: the pilot tone
head (Figure 10).
To expand on this: in order to exclude any sync
variations in studio operation, for instance from
drift, the sep-mag (perfo) sound track material
had precisely the same format and perforations
as the film stock [2] (Figure 11). The film and
74874
Retronics XL
sound follower machines are driven by so-called
synchronous motors, whose rotational speed is
governed not by voltage but by frequency. Consequently the rotational speed of these motors
is identical and synchronous, hard-locked to the
AC line frequency.
The film cameras (mostly battery-driven) contained a small frequency generator that for
24 frames per second (later 25 fps) delivered a
nominal speed of exactly 50 Hz. If the camera
speed varied (resulting from many and various
mechanical parameters), the frequency altered
analogously. This frequency range was recorded
in the middle of the sound track using the aforementioned pilot tone head.
To avoid any audible audio hum the slot of this
sound head was rotated by 90 degrees, which
eliminated the tone in the wanted signal by virtually 100 percent.
When transferring a tape recording to the AC linedriven sound follower machine, this frequency
was compared against the line frequency and
used to readjust electronically either the replay
machine (in our case the Nagra) or the recording
machine. For this purpose the Nagra provided the
ability to make corrections of up to plus or minus
4 percent using the so-called Synchronizer. For
greater values suitable accessories could be used,
which happened only in extreme cases, however.
An additional function related to this was the socalled ‘Playback Procedure’, which was employed
for vocal numbers for example. Prior to starting,
the AC line frequency was recorded onto the tape
as a pilot tone. The Nagra now received one pilot
tone from the camera, compared this with the
other tone coming from the tape, leaving the
Synchronizer to correct the difference. This system proved successful for decades.
The interface in the form of various plug connectors was truly ‘open system’ and the range of
accessory devices was infinite, from large 3,000feet tape reels, through mixing desks and crystal
control devices, to wire free applications. The
initial purchase price was definitely high for the
period in question, the fully equipped version
(without carrying case and mains power supply) costing the current equivalent of $10,000.
Three gadgets should not go unmentioned: the
tape-length counter incorporated in the self-aligning roller, the stroboscope roller for speed control
and a mechanical tape cleaner in the form of a
metal shim (Figures 12 and 13).
For a machine of this calibre there were nat-
urally appropriate headphones.
At the time only the firm Beyer
Dynamic could provide the most
linear model, the so-called ‘Normal-Telefon’ (reference standard
‘phones) with 2 x 25 ohms. In
modified form these headphones
remained in use for more than 50
years!
This recorder was a mono device
(see inset). Later the stereo version followed of course and in the
early days of the video era a version with timecode. At the end
of the 1980s digital technology
was still in its infancy but already
in 1992 there appeared a digital
version, which recorded four PCM
tracks on standard tape and this
with an unbelievable 24 bits!
Naturally development continues to
move forward; today for instance
there is a Nagra with flash memory
and all the parameters necessary
for modern digital sound recording!
(120570)
Internet Links
[1] www.ips.org.uk/faq/index.
php?title=Tonader_Power
[2] http://en.wikipedia.org/wiki/
Sound_follower
Retronics is a monthly section covering vintage electronics including legendary
Elektor designs. Contributions, suggestions and requests are welcome, please
telegraph [email protected].
Why mono?
In case anyone is wondering why you would wish to use a mono device,
here’s the explanation. If you wish to record authentic speech with a
stereo microphone or two spatially separated mikes, the sound source
needs to occupy a defined position in the virtual acoustic listening
room. If you now, as is common in films, alter the pick-up angle or the
distances within the scene, effectively this creates a new position in the
room. Human hearing registers spatial changes with great accuracy,
which is why an edit made after this move could cause listeners/viewers
irritation. A dissolve or cross-fade would not to disguise this change
either. Therefore in practice the (mono) speech does not gain its final
position in the room until the sound mixing stage. The end product is
perfected by mixing the speech together with multi-channel ‘effects’
sound recorded spatially.
11
12
13
74874
magazine
Hexadoku
Puzzle with an electronic touch
In the rare case of not being out about buying presents or clearing snow (Aussies: BBQ’ing on the beach), why
not relax for a while with this new Hexadoku brain teaser.
Enter the right numbers or letters A-F in the open boxes, find the solution in the grey boxes, send it to us and
you automatically enter the prize draw for one of four Elektor Shop vouchers.
The Hexadoku puzzle employs numbers in the hexadecimal
range 0 through F. In the diagram composed of 16 × 16 boxes,
enter numbers such that all hexadecimal numbers 0 through F
(that’s 0-9 and A-F) occur once only in each row, once in each
column and in each of the 4×4 boxes (marked by the thicker
black lines). A number of clues are given in the puzzle and
these determine the start situation.
Correct entries received enter a prize draw. All you need to do
is send us the numbers in the grey boxes.
Solve Hexadoku and win!
Participate!
Correct solutions received from the entire Elektor readership
automatically enter a prize draw for one Elektor Shop voucher worth
£80.00 and three Elektor Shop Vouchers worth £40.00 each, which
should encourage all Elektor readers to participate.
send your solution (the numbers in the grey boxes) by email to
Before January 1, 2013,
[email protected]
Prize winners
The solution of the October 2012 Hexadoku is: 75E2B. The Elektor £80.00 voucher has been awarded to Steve Hasko (UK).
The Elektor £40.00 vouchers have been awarded to Michael Franke (Germany), Jean-Paul Lagaisse (Belgium), and Franz Maurer (Netherlands).
Congratulations everyone!
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The competition is not open to employees of Elektor International Media, its business partners and/or associated publishing houses.
1
4 D
74874
www.elektor-projects.com
elektor
labs
Sharing Electronics Projects
Elektor.LABS is an online community for
people passionate about electronics. Here
you can share your projects and participate in those created by others. It’s a
place where you can discuss project
development and electronics.
Elektor’s team of editors and engineers
assist you to bring your projects to a good
end. They can help you write an article to
be published in Elektor.MAGAZINE or even
develop a complete product that you can
sell in Elektor.STORE!
GET
ELEKTORIZED
Join or Create a Project at www.elektor-labs.com
Adv Elektor labs 121101 UK.indd 1
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74874
Next month in Elektor
Jumbo size January & February 2013 edition with a ton of ideas, tips, and projects
VHF Airband Scanner
Mini Multitester
USB I/O Interface Cable *
Many aircraft enthusiasts have great interest
in following the voice communication between
aircraft and air traffic control towers. With
this receiver, you can tune into all traffic in
the 108-137 MHz VHF civil aviation band. It
is easy to build, has only one mechanical
adjustment and can even be operated from a
PC with a USB connection. A single conversion
VHF-FM receiver IC is used, which is tweaked
to function as an AM receiver by clever use of
the signal strength detector output.
You’re busy with a microcontroller project and
all sorts of things should be measured, such
as output voltages, logic levels, pulses count
and so on. What instrument to use? With this
handy multi tester you have a versatile measuring device that combines a large number
of functions in a small enclosure that you can
stick with one hand. The device acts as a logic
tester, voltmeter, pulse counter, TTL/UART
receiver and transmitter, frequency meters
and much more.
Surely it’s useful to employ the USB connection for your own measurements and control
purposes. We developed an interface cable
based on a USB-TTL cable from FTDI, to
which a small PCB with an R8C microcontroller is added for fitting into a DB25 plug
housing. The controller handles the communication with the PC, and at the output side
offers 24 pins for the user to configure and do
a variety of measuring and switching tasks.
* We regret that this article could not be published in the current
issue as planned, also for ‘USB I/O Interface Cable’.
Article titles and magazine contents subject to change; please check the Magazine tab at www.elektor.com
Elektor USA January & February 2013 edition published January 9, 2013.
See what’s brewing
@ Elektor Labs 24/7
Check out
www.elektor-labs.com
and join, share, participate!
74874
Create complex electronic systems
in minutes using Flowcode 5
Design – Simulate – Download
Flowcode is one of the World’s most advanced
graphical programming languages for microcontrollers (PIC, AVR, ARM and dsPIC/PIC24).
The great advantage of Flowcode is that it allows
those with little experience to create complex electronic systems in minutes. Flowcode’s graphical
development interface allows users to construct a
complete electronic system on-screen, develop a
program based on standard flow charts, simulate
the system and then produce hex code for PIC
AVR, ARM and dsPIC/PIC24 microcontrollers.
Convince yourself.
Demo version, further
information and ordering at
NEW!
Flowcode 5
for AVR
www.elektor.com/flowcode
Elektor RF & Microwave
Toolbox
%%%
for Android
hameg.com/xmas2012
The RF & Microwave Toolbox contains
34 calculation and conversion tools for
RF, microwave and electronics in general.
Whether you are an RF professional,
radio-amateur, astronomer or hobbyist,
this app puts some of the most important tools right at your fingertips. Literally!
Highlights:
• Amplifier cascade (NF, Gain, P1db,
OIP2, OIP3)
• Field intensity and power density
Download
converter (W/m2, V/m, A/m,
Tesla, Gauss,dBm, W)
your app now!
• PCB Trace calculator
(impedance/dimensions)
• PI and T attenuator
• Antenna temperature (Kelvin)
• EMC (EIRP, ERP, dBμV/m)
• Filter Design (Butterworth, Chebyshev, prototype)
• And much more
Further information at
www.elektor.com/rf-app
m//rf
NOVA advert page.indd 1
12-11-12 09:05
74874
Elektor Store
3
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The world’s first book with NFC technology
integrated inside
1
microcontroller based projects using the CAN bus.
You will learn how to design microcontroller based
Catch the Sun
CAN bus nodes, build a CAN bus, develop high-
LabWorX 2
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Mastering Surface
Mount Technology
The oldest known contactless connectivity technology
level programs, and then exchange data in real-
This book takes you on a crash course in techniques,
dates back 2000 years to the Han dynasty in China.
time over the bus. You will also learn how to build
tips and know-how to successfully introduce surface
In that era, the Kongming lantern was invented: a
microcontroller hardware and interface it to LEDs,
mount technology in your workflow. Even if you are
small hot air balloon used primarily for transmitting
LCDs, and A/D converters.
on a budget you too can jumpstart your designs
military signals. The Kongming balloons have today
260 pages • ISBN 978-1-907920-04-2
with advanced fine pitch parts. Besides explaining
been replaced by chips. Near Field Communication,
£29.50 • US $47.60
methodology and equipment, attention is given to
or NFC, provides wireless connectivity over short
distances based on semiconductor technology. This
book links both technologies together.
Catch the Sun is the world’s first book with NFC
semiconductor technology integrated inside, while the
SMT parts technologies and soldering methods. Many
More than 75,000 components
3
CD Elektor’s Components
Database 7
practical tips and tricks are disclosed that bring
surface mount technology into everyone’s reach
without breaking the bank. A comprehensive kit of
parts comprising all SMT components, circuit boards
content of this high-tech book is about the beautiful
This CD-ROM gives you easy access to design data
and solder stencils is available for readers wishing to
magic of low-tech ballooning. The book has multiple
for over 11,100 ICs, 37,000 transistors, FETs,
replicate three projects described in this book.
NFC chips inside that allow the book to connect to the
thyristors and triacs, 25,100 diodes and 2,000
282 pages • ISBN 978-1-907920-12-7
internet, simply by touching an NFC-hotspot in the
optocouplers. The program package consists of
£29.50 • US $47.60
book with your NFC-enabled smartphone or tablet.
eight databanks covering ICs, transistors, diodes
128 pages • ISBN 978-9-07545-861-9
and optocouplers.
£35.50 • US $57.50
A further eleven applications cover the calculation
of, for example, zener diode series resistors, voltage
regulators, voltage dividers and AMV’s. A colour
Free mikroC compiler CD-ROM included
Dual-layer DVD: 165 mins. video
5
DVD Modern Valve
Electronics
band decoder is included for determining resistor
This filmed seminar (presented by Menno van der Veen)
and inductor values. All databank applications are
starts with a short discussion of the classic approach using
fully interactive, allowing the user to add, edit and
valve load line graphs, followed by current sources and
The aim of the book is to teach you the basic principles
complete component data.
current foldback techniques. Next, the negative effect of
of CAN networks and in addition the development of
ISBN 978-90-5381-298-3 • £24.90 • US $40.20
cathode electrolytics is covered as well as reducing supply
2
Controller Area
Network Projects
Elektor Store UK 12-2012.indd 82
09-11-12 11:36
74874
Books, CD-ROMs, DVDs, Kits & Modules
8
5
7
6
9
Meet BOB
voltage interference. With the help of state of the art
an easily-understandable manner. For the interested
measurement techniques the (in)correctness of feedback
musician (and others), this book unveils, in a simple
is proven, while also clarifying what’s happening deep
and well-grounded way, what have, until now, been
within the core of the output transformer.
regarded as manufacturer secrets. The examination
You’ll be surprised first and foremost by the size
ISBN 978-1-907920-10-3 • £24.90 • US $40.20
explores deep within the guitar, including pickups and
of this USB/serial converter – no larger than the
electrical environment, so that guitar electronics are
moulded plug on a USB cable! And you’re also bound
no longer considered highly secret. With a few deft
to appreciate that fact that it’s practical, quick to
interventions, many instruments can be rendered
implement, reusable, and multi-platform – and yet
more versatile and made to sound a lot better – in the
for all that, not too expensive! Maybe you don’t think
If your USB device ever suffers from noise caused by
most cost-effective manner.
much of the various commercially-available FT232R-
an earth loop or if you want to protect your PC against
287 pages • ISBN 978-1-907920-13-4
based modules. Too expensive, too bulky, badly
external voltages then you need a USB isolator. The
£29.50 • US $47.60
designed, That’s why this project got designed in the
Avoid interference and earth loops
6
USB Isolator
circuit described in Elektor’s October 2012 edition
lines as well as the supply lines between the PC and
Free Software CD-ROM included
the USB device.
8
Art.# 120291-91 • £62.30 • US $101.40
Elementary Course
BASCOM-AVR
have already published many interesting applications
7 Electric Guitar
What would today’s rock and pop music be without
electric lead and bass guitars? These instruments
have been setting the tone for more than forty years.
Their underlying sound is determined largely by their
electrical components. But, how do they actually
work? This book answers many questions simply, in
PCB, assembled and tested
Art.# 110553-91 • £12.90 • US $20.90
The Atmel AVR family of microcontrollers are extremely
versatile and widely used. In Elektor magazine we
Sound Secrets and Technology
FT232R USB/
Serial Bridge/BOB
form of a breakout board (BOB).
offers an optimal electrical isolation of both the data
Populated and tested Board
9
employing an ATmega or ATtiny microcontroller.
The majority of these projects perform a particular
function. In this book we focus more on the software
aspects. Using lots of practical examples we show how,
using BASCOM, you can quickly get your own design
ideas up and running in silicon.
224 pages • ISBN 978-1-907920-11-0
£34.95 • US $56.40
More information on the
Elektor Website:
www.elektor.com/store
Elektor
78 York Street
London - W1H 1DP
United Kingdom
Tel.: +44 20 7692 8344
Elektor Store UK 12-2012.indd 83
09-11-12 11:36
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WITH PROTEUS PCB DESIGN
Our completely new manual router makes placing tracks quick and intuitive. During track
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Labcenter Electronics Ltd. 53-55 Main Street, Grassington, North Yorks. BD23 5AA.
Registered in England 4692454 Tel: +44 (0)1756 753440, Email: [email protected]
Naamloos-9 1
Visit our website or
phone 01756 753440
for more details
30-10-12 13:36

elektor labs

Transcription

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